test: support unreleased V8 versions

Change the RegExp in test-process-versions so that the test can pass
with V8 versions that have no patch number.

PR-URL: #12619
Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-process-versions.js

@@ -26,5 +26,5 @@ assert(/^\d+\.\d+\.\d+(-.*)?$/.test(process.versions.http_parser));
 assert(/^\d+\.\d+\.\d+(-.*)?$/.test(process.versions.node));
 assert(/^\d+\.\d+\.\d+(-.*)?$/.test(process.versions.uv));
 assert(/^\d+\.\d+\.\d+(-.*)?$/.test(process.versions.zlib));
-assert(/^\d+\.\d+\.\d+\.\d+$/.test(process.versions.v8));
+assert(/^\d+\.\d+\.\d+(\.\d+)?$/.test(process.versions.v8));
 assert(/^\d+$/.test(process.versions.modules));