update dependencies for example application

Author: sajmoon

examples/simpleapp/mix.lock

@@ -1,4 +1,5 @@
-%{"cowboy": {:hex, :cowboy, "1.0.0"},
-  "cowlib": {:hex, :cowlib, "1.0.1"},
-  "plug": {:hex, :plug, "0.11.3"},
-  "ranch": {:hex, :ranch, "1.0.0"}}
+%{"cowboy": {:hex, :cowboy, "1.0.4"},
+  "cowlib": {:hex, :cowlib, "1.0.2"},
+  "plug": {:hex, :plug, "1.1.3"},
+  "poison": {:hex, :poison, "2.1.0"},
+  "ranch": {:hex, :ranch, "1.2.1"}}