Bug in file path when using default values

[r4ulill0]

Both of these lines are the same

        PestTester::new("tests/pest",".txt", Rule::calendar, HashSet::new());
        PestTester::from_defaults(Rule::calendar, HashSet::new());

but the dot in ".txt" conflicts with this join.

We end up having tests/pest/mytest..test which is not what one should expect from defaults values.

There are 2 possible solutions, remove the dot in the join I mentioned before or remove it from the default file extension here.

If pest-test-gen is working properly with defaults maybe there is a bug there too.