Ignore swag file from root dir only (#775)

* Ignore swag file from root dir only

The rule `swag` matches not only file in main directory but also folder in `cmd/swag`.
I've changed it to match only in current folder. For visual I've changed also `swag.exe`.

I've run into issue when I tried to vendor sources for swag but also for tool. The main.go got ignored by git, I was required to `git add -f vendor/github.com/swaggo/swag/cmd/swag/main.go`

* Properly .gitignore from main folder only.

.gitignore

@@ -16,5 +16,5 @@ cover.out
 # Etc
 .DS_Store
 
-swag
-swag.exe
+/swag
+/swag.exe