Make default filter case insensitive
Make default filter case insensitive

We had an issue where for one developer SimpleCov just wouldn't work.   Turns out that in his terminal he had cded to c:\... instead of C:\... (Note the lowercase vs capital C).   Well Windows happiliy changes the prompt to lowercase.  This causes SimpleCov.root to start with a lowercase c:/.  And that causes the default filter regex to fail for every file.  Making the regex case insensitive solves this problem.  May also solve several other issues such as #77.
ptashman/simplecov,hugopeixoto/simplecov,colszowka/simplecov,QuickPay/simplecov,mallikarjunayaddala/simplecov,gerry3/simplecov,irfanah/simplecov,playpasshq/simplecov,colszowka/simplecov