Fix a flake8 warning concerning an invalid escape sequence '\.'.

This commit fixes the following flake8 warning:

    regression_tests/parsers/fileinfo_output_parser.py:112:51: W605 invalid escape sequence '\.'

It seems to me that the flake8 parser is wrong here, as the following two
strings should be equivalent, but flake8 reports a warning for the first one
but not for the second one:

    r'.*GCC.*4\.7.*'
    '.*GCC.*4\\.7.*'

Author: s3rvac

regression_tests/parsers/fileinfo_output_parser.py

@@ -109,7 +109,7 @@ class FileinfoOutput(Text):
 
     .. code-block:: python
 
-        assert fileinfo_output.contains(r'.*GCC.*4\.7.*')
+        assert fileinfo_output.contains('.*GCC.*4\\.7.*')
 
     The behavior of the ``in`` operator depends on the format of the output.
     For plain-text output, it behaves like regular ``in`` for strings,