Remove non-breaking space from library_glfw.js

See https://github.com/kripken/emscripten/blob/70173560dc471ed8d72eb834bba9c28d2507d828/src/library_glfw.js#L579 - github actually highlights the nbsp.

Example of the nbsp in master:
```
emsdk_portable/emscripten/master $ grep -bF 'GLFW.cancelFullScreen' src/library_glfw.js
21813:          GLFW.cancelFullScreen();
emsdk_portable/emscripten/master $ dd if=src/library_glfw.js bs=1 skip=21803 count=9 2>/dev/null | xxd
0000000: 7d20 656c 7365 c2a0 7b                   } else..{
```

This causes (at least) my version of Chromium to choke.