Fix Cowboy version in the getting started chapter

doc/src/guide/getting_started.asciidoc

@@ -69,7 +69,7 @@ fetch and compile Cowboy:
 PROJECT = hello_erlang
 
 DEPS = cowboy
-dep_cowboy_commit = 2.4.0
+dep_cowboy_commit = 2.5.0
 
 DEP_PLUGINS = cowboy