chore: Pass Node versions as strings to Travis

Node versions, as most versions, are strings, not numbers. 0.10 as a number
equals 0.1 which by the virtue of nvm is matched as 0.10 but shouldn't be
relied upon. Also, it screws Node numbering in Travis runs, see e.g.:
https://travis-ci.org/karma-runner/grunt-karma/builds/28585432
fix: Log errors in the background subprocess

Currently there is not output if the background subprocess exits with an error,
for example because the configuration file has a syntax error. This commit fixes
that.
docs(readme): svg badge
fix: Pass node-specific command line params to the subprocess

This commit makes the karma task pass Node-specific parameters used to start
the Node process to its background subprocess. This is required e.g. to be able
to use the --harmony flag.

Similar pull request for Grunt itself (already merged):
https://github.com/gruntjs/grunt/pull/877
release 0.9.0
chore: Update changelog for 0.9.0.
chore: Add dependency status images to the readme.
chore: Update readme to reflect the recent version bump.
docs(readme): Add singleRun option in Grunt Watch Session

Specifying the `singleRun: false` option in Grunt Watch Session to ensure people get the example working even if the karma config file specify `singleRun: true`. With singleRun set to true, the example will fail because the server is stopped after each test run.

Closes #49, #114
fix(runner): debug for background process

inherit debug for background process

Closes #10 #49