permit single quotes if they quote literal double quotes

[jackwasey]

A legitimate use of a single quote pair in R is to quote a literal double quote. This tiny patch allows this. It's not immediately clear to me how to test a negative with your check_lint tests. Thanks.

[coveralls]

Coverage decreased (-5.01%) when pulling 1b8c98b on jackwasey:master into 1f85019 on jimhester:master.

[jimhester]

Thank you very much for the patch.

Could you make the following changes.

1. Please use rex to construct the regular expression.

   • The equivalent rex expression to the regex you wrote is

   rex(start, single_quote, any_non_double_quotes, single_quote, end)

2. Please add at least one additional test to tests/testthat/test-single_quotes_linter.R showing the new functionality.

   • You can test that a given linter does not return any lints by passing NULL as the second argument.
   • So an acceptable test would be

   expect_lint('quote "something"', NULL, single_quotes_linter)

Thanks!

[coveralls]

Coverage decreased (-5.01%) when pulling b1a9d4b on jackwasey:master into 1f85019 on jimhester:master.

[jackwasey]

Think that should do it. Thanks.

[jimhester]

Thanks!