Support community PR builds

## Changes:

- Fix PR builds on Travis that do not have access to secure env vars

version.js

@@ -2,6 +2,7 @@ const request       = require('sync-request');
 const appveyorBuild = process.env.APPVEYOR_BUILD_NUMBER || '';
 const travisBuild   = process.env.TRAVIS_BUILD_NUMBER   || '';
 const commit        = process.env.TRAVIS_COMMIT         || '';
+const travisPr      = process.env.TRAVIS_PULL_REQUEST   || 'false';
 
 // ignore local builds
 if (!appveyorBuild && !travisBuild) {
@@ -10,6 +11,13 @@ if (!appveyorBuild && !travisBuild) {
    return;
 }
 
+// ignore community PR builds
+if (!process.env.GH_TOKEN && travisPr !== 'false') {
+   console.info('Travis PR build, using version', 'pr-' + travisPr);
+   module.exports = 'pr-' + travisPr;
+   return;
+}
+
 // fail build if no GH_TOKEN present
 if (!process.env.GH_TOKEN) {
    throw Error('Missing environment variable GH_TOKEN');
@@ -42,4 +50,4 @@ if (appveyorBuild) {
 } else {
    console.info('Using Travis build as version', travisVersion);
    module.exports = travisVersion;
-}
+}