Make `testRegex` Jest config a string instead of array.
Make `testRegex` Jest config a string instead of array.

Ref. https://facebook.github.io/jest/docs/configuration.html#testregex-string.

Closes #10.

lydell/prettier,Skywalker13/prettier-space-parenthesis,rattrayalex/prettier,azz/prettier,azz/prettier,Pajn/prettier,lydell/prettier,arijs/prettier-miscellaneous,azz/prettier,vjeux/prettier,prettier/prettier,lydell/prettier,existentialism/prettier,Skywalker13/prettier-space-parenthesis,jlongster/prettier,Skywalker13/prettier-space-parenthesis,prettier/prettier,existentialism/prettier,lydell/prettier,arijs/prettier-miscellaneous,arijs/prettier-with-tabs,yamafaktory/prettier,Skywalker13/prettier-space-parenthesis,arijs/prettier-with-tabs,arijs/prettier-miscellaneous,azz/prettier,despairblue/prettier,rattrayalex/prettier,danharper/prettier,existentialism/prettier,despairblue/prettier,yamafaktory/prettier,Pajn/prettier,prettier/prettier,rattrayalex/prettier,existentialism/prettier,arijs/prettier-miscellaneous,prettier/prettier