Fix erroneous directory reads

[DanPurdy]

The default glob pattern globs **/*.scss which means it would in rare cases return a path which is a directory.

For example with the following structure. /o.scss/p.scss it would return ['o.scss', 'p.scss'] as our matching glob array.

This structure can actually be found in sass-graph, a dependency of node-sass, so if you were to run sass-lint without any project specific paths/globs then you would most likely start to lint your node modules which very probably include node-sass.

I believe this is the main reason for #555

The fix is simply to pass the nodir option to glob when it syncs our array of files to lint.

I benchmarked it against doing our own fs.statSync calls and it was massively faster as expected.

Added tests for the CLI and main.

Fixes #555

<DCO 1.1 Signed-off-by: Dan Purdy [email protected]>

[coveralls]

Coverage remained the same at 97.271% when pulling 24c9a59 on DanPurdy:feature/fix-directory-reads into b2f8523 on sasstools:develop.

[coveralls]

Coverage remained the same at 97.271% when pulling 44ad9ac on DanPurdy:feature/fix-directory-reads into b2f8523 on sasstools:develop.

[coveralls]

Coverage remained the same at 97.271% when pulling 63b427e on DanPurdy:feature/fix-directory-reads into b2f8523 on sasstools:develop.

[coveralls]

Coverage remained the same at 97.271% when pulling d3c9b31 on DanPurdy:feature/fix-directory-reads into 4970c3c on sasstools:develop.