Improve performance of lines classifier

Prefer `Regexp#match?` over `String#=~` which improves the speed
by ~50% for these methods.

Author: splattael

lib/simplecov/lines_classifier.rb

@@ -17,14 +17,14 @@ def self.no_cov_line
     end
 
     def self.no_cov_line?(line)
-      line =~ no_cov_line
+      no_cov_line.match?(line)
     rescue ArgumentError
       # E.g., line contains an invalid byte sequence in UTF-8
       false
     end
 
     def self.whitespace_line?(line)
-      line =~ WHITESPACE_OR_COMMENT_LINE
+      WHITESPACE_OR_COMMENT_LINE.match?(line)
     rescue ArgumentError
       # E.g., line contains an invalid byte sequence in UTF-8
       false