rules: only check case of first word after subsystem

The first colon denotes the subsystem(s). Any further colons are part of the title and should not be subject to the rule that the following word be in lowercase.
richardlau · Feb 28, 2019 · Feb 27, 2019 · Feb 27, 2019 · 60609b7c2e668bb288b7ee274369b9e8034716b5
commit 60609b7c2e668bb288b7ee274369b9e8034716b5
diff --git a/lib/rules/title-format.js b/lib/rules/title-format.js
@@ -52,7 +52,7 @@ module.exports = {
       }
     }
 
-    const result = /^(.+?): [A-Z]/.exec(context.title)
+    const result = /^([^:]+?): [A-Z]/.exec(context.title)
     if (result) {
       context.report({
         id: id

diff --git a/test/rules/title-format.js b/test/rules/title-format.js
@@ -77,5 +77,43 @@ test('rule: title-format', (t) => {
     tt.end()
   })
 
+  t.test('first word after subsystem should be in lowercase', (tt) => {
+    tt.plan(2)
+    const context = makeCommit('test: Some message')
+
+    context.report = (opts) => {
+      tt.pass('called report')
+      tt.strictSame(opts, {
+        id: 'title-format'
+      , message: 'First word after subsystem(s) in title should be lowercase.'
+      , string: 'test: Some message'
+      , line: 0
+      , column: 7
+      , level: 'fail'
+      })
+    }
+
+    Rule.validate(context)
+    tt.end()
+  })
+
+  t.test('colon in message followed by uppercase word', (tt) => {
+    tt.plan(2)
+    const context = makeCommit('test: some message: Message')
+
+    context.report = (opts) => {
+      tt.pass('called report')
+      tt.strictSame(opts, {
+        id: 'title-format'
+      , message: 'Title is formatted correctly.'
+      , string: ''
+      , level: 'pass'
+      })
+    }
+
+    Rule.validate(context)
+    tt.end()
+  })
+
   t.end()
 })