Run "tools" job on PR when commit message starts with "Update RLS/miri/..."

Author: kennytm

.travis.yml

@@ -169,7 +169,7 @@ matrix:
     - env: IMAGE=x86_64-gnu-aux
       if: branch = auto
     - env: IMAGE=x86_64-gnu-tools
-      if: branch = auto
+      if: branch = auto OR (type = pull_request AND commit_message =~ /(?i:^update.*\b(rls|rustfmt|clippy|miri)\b)/)
     - env: IMAGE=x86_64-gnu-debug
       if: branch = auto
     - env: IMAGE=x86_64-gnu-nopt