Fix parameters handling with implicit spec files

If no spec patterns are presented, rspec will run with empty spec list. This bug can demonstrated like this(taken from my work-related repo):
```
% rspec
....................................................................................................................................................................................................................................................................................................................

Finished in 14.48 seconds (files took 3.59 seconds to load)
308 examples, 0 failures
```
and
```
% bin/rspec --fail-fast
No examples found.


Finished in 0.0007 seconds (files took 21.11 seconds to load)
0 examples, 0 failures
```
It fails really fast indeed :smile: 
Update:
```
% spring stop; bin/rspec --fail-fast
Spring stopped.
"gems/rspec-core-3.0.4/exec/rspec's $0: rspec --fail-fast"
"command: rspec --fail-fast"
No examples found.


Finished in 0.00098 seconds (files took 0.76091 seconds to load)
0 examples, 0 failures
```
It seems that `$0` doesn't really work the way we expect.