freeze version of execjs
freeze version of execjs

- Rubinius build is currently failing with the latest version of execjs
- Execjs is used for tests written in coffee script

amandamholl/jasmine-gem,mavenlink/jasmine-gem,brigade/jasmine-gem,amandamholl/jasmine-gem,mavenlink/jasmine-gem,amandamholl/jasmine-gem,brigade/jasmine-gem,mavenlink/jasmine-gem,brigade/jasmine-gem