Reverting 'brew.sh' to origin/master to resolve conflict

Library/Homebrew/brew.sh

@@ -73,6 +73,18 @@ fi
 export GEM_OLD_HOME="$GEM_HOME"
 export GEM_OLD_PATH="$GEM_PATH"
 
+# Users may have these set, pointing the system Ruby
+# at non-system gem paths
+unset GEM_HOME
+unset GEM_PATH
+
+# Users may have this set, injecting arbitrary environment changes into
+# bash processes inside builds
+unset BASH_ENV
+
+# Users may have this set, breaking grep's output.
+unset GREP_OPTIONS
+
 HOMEBREW_SYSTEM="$(uname -s)"
 case "$HOMEBREW_SYSTEM" in
   Darwin) HOMEBREW_MACOS="1" ;;