Fixed typos in GenServer.Behaviour docs
Fixed typos in GenServer.Behaviour docs

ggcampinho/elixir,antipax/elixir,antipax/elixir,kelvinst/elixir,kelvinst/elixir,joshprice/elixir,kimshrier/elixir,pedrosnk/elixir,gfvcastro/elixir,beedub/elixir,ggcampinho/elixir,michalmuskala/elixir,pedrosnk/elixir,kimshrier/elixir,gfvcastro/elixir,elixir-lang/elixir,lexmag/elixir,lexmag/elixir,beedub/elixir