fix: convert only first line of commit message to lowercase (#779)

Helps #777

lib/workers/branch/commit.js

@@ -13,7 +13,9 @@ async function commitFilesToBranch(config) {
     logger.debug(`${updatedFiles.length} file(s) to commit`);
     let commitMessage = handlebars.compile(config.commitMessage)(config);
     if (config.semanticCommits) {
-      commitMessage = `${config.semanticPrefix} ${commitMessage.toLowerCase()}`;
+      const splitMessage = commitMessage.split('\n');
+      splitMessage[0] = splitMessage[0].toLowerCase();
+      commitMessage = `${config.semanticPrefix} ${splitMessage.join('\n')}`;
     }
     // API will know whether to create new branch or not
     await config.api.commitFilesToBranch(

test/workers/branch/commit.spec.js

@@ -41,5 +41,18 @@ describe('workers/branch/automerge', () => {
       expect(config.api.commitFilesToBranch.mock.calls.length).toBe(1);
       expect(config.api.commitFilesToBranch.mock.calls).toMatchSnapshot();
     });
+    it('lowercases only the first line when applying semantic prefix', async () => {
+      config.updatedPackageFiles.push({
+        name: 'package.json',
+        contents: 'some contents',
+      });
+      config.commitMessage = 'Foo\n\nBar';
+      config.semanticCommits = true;
+      await commitFilesToBranch(config);
+      expect(config.api.commitFilesToBranch.mock.calls.length).toBe(1);
+      expect(config.api.commitFilesToBranch.mock.calls[0][2]).toEqual(
+        'some-prefix foo\n\nBar'
+      );
+    });
   });
 });