cmd/ebitenmobile: Bug fix: .exe was requried on Windows
cmd/ebitenmobile: Bug fix: .exe was requried on Windows

On Windows, executable files must have .exe extension, or
exec.LookPath since exec.LookPath checks %PATHEXT%.

This fixes the issue that ebitenmobile didn't invoke the original
gobind wrapper and then didn't include and compile some Java files.

Fixes #1096

hajimehoshi/ebiten,hajimehoshi/ebiten