Fix incorrect detection of rspec file when file is open within a folder on windows

On windows, when a rspec file is open within a folder, the method find_partition_folder raised an error: invalid regex due to \\ as file separator
Syntax error, so I belive it's typo
Other two OS also have similar typo
Add support for tests with prefix 'test_' in their filename
Merge pull request #204 from Eric-Guo/patch-1

Syntax error, so I belive it's typo
Merge pull request #197 from legallth17/patch-1

Fix incorrect detection of rspec file when  open within a folder on windows
':' is a valid character for a MiniTest test name
Merge pull request #207 from modosc/master

':' is a valid character for a MiniTest test name
Merge pull request #202 from neocsr/test_prefix

Add support for tests with prefix 'test_' in their filename