Update api.github.com certificate signature

[earlephilhower]

Fixes #5144

[earlephilhower]

There is another axTLS problem with the new GH certs, but the SHA1 fingerprint works. Actual CA checking reports and error:

SDK:2.2.1(cfd48f3)/Core:2.4.2-40-gcd43337/lwIP:2.0.3(STABLE-2_0_3_RELEASE/glue:arduino-2.4.1-13-g163bb82)/BearSSL:6d1cefc

connecting to NOBABIES
sta config unchangedscawifi evt: 2
ndone
scandone
state: 0 -> 2 (b0)
state: 2 -> 3 (0)
state: 3 -> 5 (10)
add 0
aid 5
cnt 

connected with NOBABIES, channel 10
dhcp client start...
wifi evt: 0
..ip:192.168.1.138,mask:255.255.255.0,gw:192.168.1.1
wifi evt: 3
.
WiFi connected
IP address: 
192.168.1.138
Setting time using SNTP.
Current time: Tue Sep 18 09:23:58 2018
=== CERTIFICATE ISSUED TO ===
Common Name (CN):		DigiCert High Assurance EV Root CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Basic Constraints:		critical, CA:TRUE, pathlen:10000
Key Usage:			critical, Encipher Only
=== CERTIFICATE ISSUED BY ===
Common Name (CN):		DigiCert High Assurance EV Root CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Not Before:			Fri Nov 10 00:00:00 2006
Not After:			Mon Nov 10 00:00:00 2031
RSA bitsize:			2048
Sig Type:			SHA1
connecting to api.github.com
[hostByName] request IP for: api.github.com
[hostByName] Host: api.github.com IP: 192.30.255.117
:ref 1
:ref 2
State:	sending Client Hello (1)
:wr 95 95 0
:wrc 95 95 0
:ack 95
:rn 536
:rch 536, 536
:rch 1072, 536
:rch 1608, 536
:rd 5, 2144, 0
:rdi 536, 5
:rd 80, 2144, 5
:rdi 531, 80
State:	receiving Server Hello (2)
:rd 5, 2144, 85
:rdi 451, 5
:rd 2054, 2144, 90
:rdi 446, 446
:c 446, 536, 2144
:rdi 536, 536
:c 536, 536, 1608
:rdi 536, 536
:c 536, 536, 1072
:rdi 536, 536
:c0 536, 536
:rn 536
:rd 536, 536, 0
:rdi 536, 536
:c0 536, 536
:rn 269
:rd 260, 269, 0
:rdi 269, 260
State:	receiving Certificate (11)
=== CERTIFICATE ISSUED TO ===
Common Name (CN):		*.github.com
Organization (O):		GitHub, Inc.
Location (L):			San Francisco
Country (C):			US
State (ST):			California
Basic Constraints:		critical, CA:FALSE, pathlen:10000
Key Usage:			critical, Key Cert Sign, Encipher Only
Subject Alt Name:		*.github.com github.com 
=== CERTIFICATE ISSUED BY ===
Common Name (CN):		DigiCert SHA2 High Assurance Server CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Not Before:			Tue Jun 19 00:00:00 2018
Not After:			Wed Jul 10 12:00:00 2019
RSA bitsize:			2048
Sig Type:			SHA256
=== CERTIFICATE ISSUED TO ===
Common Name (CN):		DigiCert SHA2 High Assurance Server CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Basic Constraints:		critical, CA:TRUE, pathlen:0
Key Usage:			critical, Encipher Only
=== CERTIFICATE ISSUED BY ===
Common Name (CN):		DigiCert High Assurance EV Root CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Not Before:			Tue Oct 22 12:00:00 2013
Not After:			Sun Oct 22 12:00:00 2028
RSA bitsize:			2048
Sig Type:			SHA256
:rd 5, 269, 260
:rdi 9, 5
:rd 4, 269, 265
:rdi 4, 4
:c0 4, 269
State:	receiving Server Hello Done (14)
State:	sending Client Key Exchange (16)
:wr 267 267 0
:wrc 256 267 0
:wrc 11 11 0
:wr 6 6 0
:wrc 6 6 0
State:	sending Finished (16)
:wr 85 85 0
:wrc 85 85 0
:ack 267
:ack 91
:rn 91
:rd 5, 91, 0
:rdi 91, 5
:rd 1, 91, 5
:rdi 86, 1
:rd 5, 91, 6
:rdi 85, 5
:rd 80, 91, 11
:rdi 80, 80
:c0 80, 91
State:	receiving Finished (16)
=== CERTIFICATE ISSUED TO ===
Common Name (CN):		*.github.com
Organization (O):		GitHub, Inc.
Location (L):			San Francisco
Country (C):			US
State (ST):			California
Basic Constraints:		critical, CA:FALSE, pathlen:10000
Key Usage:			critical, Key Cert Sign, Encipher Only
Subject Alt Name:		*.github.com github.com 
=== CERTIFICATE ISSUED BY ===
Common Name (CN):		DigiCert SHA2 High Assurance Server CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Not Before:			Tue Jun 19 00:00:00 2018
Not After:			Wed Jul 10 12:00:00 2019
RSA bitsize:			2048
Sig Type:			SHA256
Verify:				Basic constraint invalid
=== CERTIFICATE ISSUED TO ===
Common Name (CN):		DigiCert SHA2 High Assurance Server CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Basic Constraints:		critical, CA:TRUE, pathlen:0
Key Usage:			critical, Encipher Only
=== CERTIFICATE ISSUED BY ===
Common Name (CN):		DigiCert High Assurance EV Root CA
Organization (O):		DigiCert Inc
Organizational Unit (OU):	www.digicert.com
Country (C):			US
Not Before:			Tue Oct 22 12:00:00 2013
Not After:			Sun Oct 22 12:00:00 2028
RSA bitsize:			2048
Sig Type:			SHA256
Verify:				Certificate verify successful
ssl_verify_cert returned -523
Error: Basic constraint invalid
ERROR: certificate verification failed!

That's another problem, axTLS related.