bump simplecov to avoid segfault

Gemfile

@@ -183,7 +183,7 @@ group :test do
 
   # why in Gemfile? see: https://github.com/guard/guard-test
   gem 'ruby-prof'
-  gem 'simplecov', require: false
+  gem 'simplecov', '~> 0.12.0', require: false
   gem 'shoulda-matchers', '~> 3.1', require: nil
   gem 'json_spec'
   gem 'activerecord-tableless', '~> 1.0'

Gemfile.lock

@@ -237,7 +237,6 @@ GEM
       representable (~> 2.0)
       uber
     docile (1.1.5)
-      unf (>= 0.0.5, < 1.0.0)
     domain_name (0.5.20160826)
       unf (>= 0.0.5, < 1.0.0)
     equalizer (0.0.11)
@@ -515,9 +514,9 @@ GEM
     shoulda-context (1.2.1)
     shoulda-matchers (3.1.1)
       activesupport (>= 4.0.0)
-    simplecov (0.11.2)
+    simplecov (0.12.0)
       docile (~> 1.1.0)
-      json (~> 1.8)
+      json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
     slop (3.6.0)
@@ -683,7 +682,7 @@ DEPENDENCIES
   selenium-webdriver (~> 2.53.4)
   shoulda-context (~> 1.2)
   shoulda-matchers (~> 3.1)
-  simplecov
+  simplecov (~> 0.12.0)
   sprockets (~> 3.5.2)
   sqlite3
   stringex (~> 2.6.1)