Parse Headless Chrome versions

The initial implementation of the Headless Chrome detection (ua-parser#228) didn't detect
versions of the headless version. This has been fixed.

A test for Ubuntu Chromium in headless mode was also added. I haven't made it
recognized as HeadlessChromium as it has HeadlessChrome in the user agent. It
might be worthwhile to check how a pure compiled from source Chromium behaves.
Nevertheless, this commit is still an improvement.

regexes.yaml

@@ -383,8 +383,7 @@ user_agent_parsers:
 
   # Headless Chrome
   # https://chromium.googlesource.com/chromium/src/+/lkgr/headless/README.md
-  # Currently only available on Linux
-  - regex: 'HeadlessChrome'
+  - regex: '(HeadlessChrome)/(\d+)\.(\d+)(?:\.(\d+))?'
     family_replacement: 'HeadlessChrome'
 
   # Browser/major_version.minor_version

tests/test_ua.yaml

@@ -6657,11 +6657,17 @@ test_cases:
     minor: '7'
     patch: '10'
 
-  - user_agent_string: 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome Safari/537.36'
+  - user_agent_string: 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) HeadlessChrome/60.0.3112.78 Safari/537.36'
     family: 'HeadlessChrome'
-    major:
-    minor:
-    patch:
+    major: '60'
+    minor: '0'
+    patch: '3112'
+
+  - user_agent_string: 'Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/59.0.3071.109 HeadlessChrome/59.0.3071.109 Safari/537.36'
+    family: 'HeadlessChrome'
+    major: '59'
+    minor: '0'
+    patch: '3071'
 
   - user_agent_string: 'Roku/DVP-6.2 (096.02E06005A)'
     family: 'Roku'