Remove dot and slash before files in cmd/ipfs/.gitignore

It looks like files are not ignored when they are listed
starting with ./ in a .gitignore file.

At least this is true for me on Linux for the "ipfs"
binary in "cmd/ipfs/.gitignore".

License: MIT
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>

cmd/ipfs/.gitignore

-./ipfs
-./ipfs.exe
+ipfs
+ipfs.exe