Fix mustache command

docs/CHANGELOG.md

@@ -14,6 +14,8 @@ The format of this change log follows the advice given at [Keep a CHANGELOG](htt
   `.travis.yml` file to get Behat running again.  This is because Travis CI changed their default
   environment from Precise to Trusy.  On Trusty, the default Firefox version is 55, which is not
   compatible with Selenium.
+- Fixed `moodle-plugin-ci mustache` command when `_JAVA_OPTIONS` environment variable is set.
+  This is now set by default in Trusty builds.
 
 ### Added
 - Can now use Chrome with Behat, see [help document](Chrome.md) for details.

src/Command/MustacheCommand.php

@@ -58,9 +58,15 @@ protected function execute(InputInterface $input, OutputInterface $output)
 
         $code = 0;
         foreach ($files as $file) {
+            // _JAVA_OPTIONS is something Travis CI started to set in Trusty.  This breaks Mustache because
+            // the output from vnu.jar needs to be captured and JSON decoded.  When _JAVA_OPTIONS is present,
+            // then a message like "Picked up _JAVA_OPTIONS..." is printed which breaks JSON decoding.
             $process = $this->execute->passThroughProcess(
                 ProcessBuilder::create()
-                    ->setPrefix('php')
+                    ->add('env')
+                    ->add('-u')
+                    ->add('_JAVA_OPTIONS')
+                    ->add('php')
                     ->add($wrapper)
                     ->add('--filename='.$file)
                     ->add('--validator='.$jarFile)