Use bash for shell

This may work around a problem where kill() does not work correctly in a travis context (https://github.com/travis-ci/travis-ci/issues/704)

test/server_process.js

@@ -13,7 +13,8 @@ describe('server process', function() {
 
     console.log("launching server...")
     server_proc = child_process.spawn('yarn', ['dev'], {
-      cwd: '.'
+      cwd: '.',
+      shell: '/bin/bash'
     });
 
     server_proc.on('exit', function(code, signal) {