chore(karma): fixes coverage

[gmosteoru]

mostly reverts 30f2ea3ff2ca134513058a853ad237c3d1660818

• installs karma-coverage to fix 'grunt coverage' task
• reverts to using karma-coverage in karma.conf files; this fixes coverage when running 'grunt test'
• uninstalls karma-coverage-istanbul-reporter as it is not needed

This is done to fix the build as described in this issue https://github.com/angular-ui/ui-grid/issues/7091

[commit-lint[bot]]

Chore

• karma: fixes coverage (47c3158)
• dependencies: removes angular as a dev-dependency because it is not used (418d673)

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