Upgrade Prism version to 2.x/Latest. Fixes #755

[YoungNastyMan]

Fixes #755

Checklist

• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the [Contribution Guide] and my PR follows them.
• I updated my branch with the master branch.
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation about the functionality in the appropriate .md file
• I have added in line documentation to the code I modified

Short description of what this PR does:

• Switches 2 mkdir calls to one mkdir -p call (this is a minor refactor) in travis.yml
• Changes the prism:install npm script to use Prism 2.x. This might need to be updated again if prism changes the location of their install.sh
• Changes the prism npm script to work with Prism 2.x. The --list switch is no longer supported apparently
• Changes test/prism.sh to use the latest version everytime. This was commented out earlier for some reason?

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[childish-sambino]

Closing as this was fixed by #1112