Correct name for no_unnecessary_double_quotes test
Merge pull request #240 from easytobook/no-unnecessary-double-quotes

Correct name for no_unnecessary_double_quotes test
Correct name for no_unnecessary_double_quotes test
Add no_interpolation_in_single_quotes rule

While it shouldn't be a problem when good unit tests are in place, this rule
can warn developers when string interpolation is (accidentally) used in
single quoted strings.
Merge branch 'no-interpolation-in-single-quotes'