deps: github.com/aws/aws-sdk-go@6ca8a5496cb4 (#11727)

Reference: #11682
Reference: aws/aws-sdk-go#3089

The fix for widespread error handling regression was merged upstream into the AWS Go SDK, however there was not a release today on the normal daily release cadence. This pulls in the commit after AWS Go SDK v1.28.7 containing the fix for the missing error messages that was merged yesterday so we can allow the full acceptance test suite to run overnight.

Updated via:

```
go get github.com/aws/aws-sdk-go@6ca8a5496cb4723ad4ef1e6709ed593ea81ce000
go mod tidy
go mod vendor
```

Output from acceptance testing (as a smoke test of the fixed behavior):

```
--- PASS: TestAccAWSCodeBuildProject_basic (37.35s)
```

go.mod

@@ -3,7 +3,7 @@ module github.com/terraform-providers/terraform-provider-aws
 go 1.13
 
 require (
-	github.com/aws/aws-sdk-go v1.28.5
+	github.com/aws/aws-sdk-go v1.25.14-0.20200121234158-6ca8a5496cb4
 	github.com/beevik/etree v1.1.0
 	github.com/bflad/tfproviderdocs v0.4.1
 	github.com/bflad/tfproviderlint v0.7.0

go.sum

@@ -35,8 +35,8 @@ github.com/armon/go-radix v1.0.0 h1:F4z6KzEeeQIMeLFa97iZU6vupzoecKdU5TX24SNppXI=
 github.com/armon/go-radix v1.0.0/go.mod h1:ufUuZ+zHj4x4TnLV4JWEpy2hxWSpsRywHrMgIH9cCH8=
 github.com/aws/aws-sdk-go v1.15.78/go.mod h1:E3/ieXAlvM0XWO57iftYVDLLvQ824smPP3ATZkfNZeM=
 github.com/aws/aws-sdk-go v1.25.3/go.mod h1:KmX6BPdI08NWTb3/sm4ZGu5ShLoqVDhKgpiN924inxo=
-github.com/aws/aws-sdk-go v1.28.5 h1:yYeWPM8w5FoIj3Lo0BDZxRyDpTveKTq/qvnIEPBnev8=
-github.com/aws/aws-sdk-go v1.28.5/go.mod h1:KmX6BPdI08NWTb3/sm4ZGu5ShLoqVDhKgpiN924inxo=
+github.com/aws/aws-sdk-go v1.25.14-0.20200121234158-6ca8a5496cb4 h1:b7uKhMm55tbrGGyqsz1665EB6UMDEPtI0irL34/g7kk=
+github.com/aws/aws-sdk-go v1.25.14-0.20200121234158-6ca8a5496cb4/go.mod h1:KmX6BPdI08NWTb3/sm4ZGu5ShLoqVDhKgpiN924inxo=
 github.com/beevik/etree v1.1.0 h1:T0xke/WvNtMoCqgzPhkX2r4rjY3GDZFi+FjpRZY2Jbs=
 github.com/beevik/etree v1.1.0/go.mod h1:r8Aw8JqVegEf0w2fDnATrX9VpkMcyFeM0FhwO62wh+A=
 github.com/beorn7/perks v0.0.0-20180321164747-3a771d992973/go.mod h1:Dwedo/Wpr24TaqPxmxbtue+5NUziq4I4S80YR8gNf3Q=