tests: use SimpleCov 0.12.0 and Coveralls 0.8.14

SimpleCov 0.12.0 brings some moderate speed improvements and soon (sadly
not yet) can be switched back to a stable release. Update to matching
Coveralls release, fortunately with fewer dependencies than before.

Library/Homebrew/test/Gemfile

@@ -3,16 +3,19 @@ source "https://rubygems.org"
 gem "mocha", "~> 1.1"
 gem "minitest", "~> 5.3"
 gem "rake", "~> 10.3"
-# This is a patched version of the v0.11.2. Switch back to the stable version
-# when #436 has been merged upstream.
-# https://github.com/colszowka/simplecov/pull/436
-# See also https://github.com/Homebrew/legacy-homebrew/pull/48250#issuecomment-173171990
-gem "simplecov", "0.11.2",
-  :git => "https://github.com/Homebrew/simplecov.git",
-  :branch => "tracked-files-root-fix",
-  :require => false
-gem "coveralls", "0.8.10", :require => false
-# We need to pin these versions because those are the last supporting Ruby 1.8.
-# Remove these lines when we've stopped supporting it.
-gem "mime-types", "~> 1.16"
-gem "rest-client", "1.6.9"
+
+group :coverage do
+  # This is SimpleCov v0.12.0 with one PR merged on top, that finally resolves
+  # all issues with parallel tests, uncovered files, and tracked files. Switch
+  # back to stable as soon as v0.12.1 or v0.13.0 is released. See pull request
+  # <https://github.com/Homebrew/legacy-homebrew/pull/48250> for full details.
+  gem "simplecov", "0.12.0",
+    :git => "https://github.com/colszowka/simplecov.git",
+    :branch => "master", # commit 257e26394c464c4ab388631b4eff1aa98c37d3f1
+    :require => false
+  gem "coveralls", "0.8.14", :require => false
+
+  # We need to pin the version of this Coveralls dependency because it is the
+  # last one to support Ruby 1.8. Remove as soon as we stop using Ruby 1.8.
+  gem "json", "~> 1.8", :require => false
+end

Library/Homebrew/test/Gemfile.lock

 GIT
-  remote: https://github.com/Homebrew/simplecov.git
-  revision: 4c7642496e902ba9028a74500971e40b3e3aaa29
-  branch: tracked-files-root-fix
+  remote: https://github.com/colszowka/simplecov.git
+  revision: 257e26394c464c4ab388631b4eff1aa98c37d3f1
+  branch: master
   specs:
-    simplecov (0.11.2)
+    simplecov (0.12.0)
       docile (~> 1.1.0)
-      json (~> 1.8)
+      json (>= 1.8, < 3)
       simplecov-html (~> 0.10.0)
 
 GEM
   remote: https://rubygems.org/
   specs:
-    coveralls (0.8.10)
-      json (~> 1.8)
-      rest-client (>= 1.6.8, < 2)
-      simplecov (~> 0.11.0)
+    coveralls (0.8.14)
+      json (>= 1.8, < 3)
+      simplecov (~> 0.12.0)
       term-ansicolor (~> 1.3)
       thor (~> 0.19.1)
       tins (~> 1.6.0)
     docile (1.1.5)
     json (1.8.3)
     metaclass (0.0.4)
-    mime-types (1.25.1)
-    minitest (5.8.4)
+    minitest (5.9.0)
     mocha (1.1.0)
       metaclass (~> 0.0.1)
     rake (10.5.0)
-    rest-client (1.6.9)
-      mime-types (~> 1.16)
     simplecov-html (0.10.0)
     term-ansicolor (1.3.2)
       tins (~> 1.0)
@@ -38,13 +34,12 @@ PLATFORMS
   ruby
 
 DEPENDENCIES
-  coveralls (= 0.8.10)
-  mime-types (~> 1.16)
+  coveralls (= 0.8.14)
+  json (~> 1.8)
   minitest (~> 5.3)
   mocha (~> 1.1)
   rake (~> 10.3)
-  rest-client (= 1.6.9)
-  simplecov (= 0.11.2)!
+  simplecov (= 0.12.0)!
 
 BUNDLED WITH
    1.11.2