Get PR number from bors commit message

Author: flip1995

.travis.yml

@@ -95,7 +95,8 @@ matrix:
 script:
   - |
     if [ "$TRAVIS_BRANCH" == "auto" ] || [ "$TRAVIS_BRANCH" == "try" ]; then
-      output=$(curl -H "Authorization: token $GITHUB_API_TOKEN" -s "https://api.github.com/repos/rust-lang/rust-clippy/pulls/$TRAVIS_PULL_REQUEST" | \
+      pr=$(echo $TRAVIS_COMMIT_MESSAGE | grep -o "#[0-9]*" | head -1 | sed 's/^#//g)
+      output=$(curl -H "Authorization: token $GITHUB_API_TOKEN" -s "https://api.github.com/repos/rust-lang/rust-clippy/pulls/$pr" | \
         python -c "import sys, json; print(json.load(sys.stdin)['body'])" | \
         grep "changelog: " | \
         sed "s/changelog: //g")