Depend on thread_safe gem in specs
Depend on thread_safe gem in specs

It's needed to test memory storage.

Note: The specs didn't fail because thread_safe is required by
many other gems which we depend on.

pxlpnk/rom,denyago/rom,cored/rom,endash/rom,dekz/rom,Snuff/rom,pvcarrera/rom,rom-rb/rom,rom-rb/rom,jeremyf/rom,kwando/rom,vrish88/rom,rom-rb/rom,dcarral/rom