Bump formtastic from 2.1.1 to 3.1.5

Bumps [formtastic](https://github.com/justinfrench/formtastic) from 2.1.1 to 3.1.5.
- [Changelog](https://github.com/justinfrench/formtastic/blob/master/CHANGELOG.md)
- [Commits](https://github.com/justinfrench/formtastic/commits)

[![Dependabot compatibility score](https://api.dependabot.com/badges/ci_status?dependency-name=formtastic&package-manager=bundler&previous-version=2.1.1&new-version=3.1.5)](https://dependabot.com/compatibility-score.html)

I'll automatically resolve any conflicts with this PR as long as you don't alter it yourself.

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Gemfile

@@ -77,7 +77,7 @@ end
 
 gem 'uuidtools', '~> 2.1'
 gem 'fastercsv', '~> 1.5.4'
-gem 'formtastic', '~> 2.1.0'
+gem 'formtastic', '~> 3.1.5'
 gem 'mustache', '1.0.5'
 gem 'rabl', '~>0.13.1'
 

Gemfile.lock

@@ -343,8 +343,8 @@ GEM
       dotenv (>= 0.7)
       thor (>= 0.13.6)
     formatador (0.2.5)
-    formtastic (2.1.1)
-      actionpack (~> 3.0)
+    formtastic (3.1.5)
+      actionpack (>= 3.2.13)
     gherkin (4.1.3)
     git (1.3.0)
     google_drive (0.3.9)
@@ -375,7 +375,7 @@ GEM
       domain_name (~> 0.5)
     httparty (0.15.6)
       multi_xml (>= 0.5.2)
-    i18n (0.8.4)
+    i18n (0.8.6)
     inflecto (0.0.2)
     ipaddress (0.8.3)
     jbuilder (2.6.4)
@@ -744,7 +744,7 @@ DEPENDENCIES
   fastercsv (~> 1.5.4)
   fog
   foreman
-  formtastic (~> 2.1.0)
+  formtastic (~> 3.1.5)
   google_drive
   guard (~> 2.14.1)
   guard-test