Update project dependencies

[azuken]

Update httpoison 0.11 to 1.2 Update poison 3.0 to 4.0 Update ex_doc 0.16 to 0.19 Update inch_ex 0.5 to 1.0 Update excoveralls 0.8 to 0.9 Update mix_test_watch 0.2 to 0.8

The project compiles and tests are passing.

[coveralls]

Coverage remained the same at 78.03% when pulling e1dd83324e5e40aea373cef1f5e64088dd68f024 on azuken:issue#58 into 3d351dad46681f35a146df30aa668c860553c551 on exponentially:master.

[burmajam]

Thanks