karma: update to version 0.12
karma: update to version 0.12

We will need this version when we begin using grunt-karma in a
subsequent commit. Unlike karma 0.10, version 0.12 no longer depends
on a number of plugins:

  https://github.com/karma-runner/karma/commit/e033d5618a98

We now explicitly depend on the plugins we use.

mgeisler/swift-browser,mindware/swift-browser,zerovm/swift-browser,mindware/swift-browser,mgeisler/swift-browser,zerovm/swift-browser