update nokogiri in response to audit:

```yaml
Name: nokogiri
Version: 1.10.4
Advisory: CVE-2019-13117
Criticality: Unknown
URL: sparklemotion/nokogiri#1943
Title: Nokogiri gem, via libxslt, is affected by multiple vulnerabilities
Solution: upgrade to >= 1.10.5
```

Gemfile.lock

@@ -146,7 +146,7 @@ GEM
     momentjs-rails (2.20.1)
       railties (>= 3.1)
     multipart-post (2.1.1)
-    nokogiri (1.10.4)
+    nokogiri (1.10.5)
       mini_portile2 (~> 2.4.0)
     parser (2.6.2.1)
       ast (~> 2.4.0)