Docs: change Dict.merge description to read more naturally
Docs: change Dict.merge description to read more naturally

Previously there was an additional "dict" - this is as a result of it
previously saying "dict `a`"

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