Remove 'cache' directories from .gitignore; Drupal 8 commits some directories with this name.

.gitignore

@@ -3,16 +3,19 @@ sites/*/files
 sites/*/private
 files/*
 private/*
-cache
 
 # Pantheon commits a settings.php for environment-specific settings.
 # Place local settings in settings.local.php
 sites/*/settings.local.php
+sites/*/services*.yml
 
 # ** Only works in OSs that support newer versions of fnmatch (Bash 4+)
 /sites/default/**/files
 /sites/default/**/private
 
+# Ignore SimpleTest multi-site environment.
+sites/simpletest
+
 # Packages #
 ############
 *.7z