Run x86_64-gnu-tools job for "update cargo" PRs since cargo can break RLS.

Author: ehuss

.travis.yml

@@ -177,7 +177,7 @@ matrix:
     - env: IMAGE=x86_64-gnu-aux
       if: branch = auto
     - env: IMAGE=x86_64-gnu-tools
-      if: branch = auto OR (type = pull_request AND commit_message =~ /(?i:^update.*\b(rls|rustfmt|clippy|miri)\b)/)
+      if: branch = auto OR (type = pull_request AND commit_message =~ /(?i:^update.*\b(rls|rustfmt|clippy|miri|cargo)\b)/)
     - env: IMAGE=x86_64-gnu-debug
       if: branch = auto
     - env: IMAGE=x86_64-gnu-nopt