Fix escript.build deps warning

[davedoesdev]

Without this, mix escript.build gives the following warning:

warning: variable "deps" does not exist and is being expanded to "deps()", please use parentheses to remove the ambiguity or change the variable name
  /home/david/centro/test/example/elixir/deps/eventsource_ex/mix.exs:10

[davedoesdev]

@cwc thanks. I've no idea why mix didn't warn about these until the deps ones were fixed but now it does:

avid@david-Latitude-E6440:~/centro/test/example/elixir/apps/subscribe$ mix escript.build
==> eventsource_ex
Compiling 2 files (.ex)
warning: variable "self" does not exist and is being expanded to "self()", please use parentheses to remove the ambiguity or change the variable name
  lib/eventsource_ex.ex:7

warning: variable "self" does not exist and is being expanded to "self()", please use parentheses to remove the ambiguity or change the variable name
  lib/eventsource_ex.ex:18

Generated eventsource_ex app

If I change self to self() then the warnings go. Would you like another PR for those?

[cwc]

That would be cool. I assume the Elixir team made the decision to prompt a more explicit code style - so that it's more obvious to the second programmer on a project that e.g. self is not merely a variable, but a function call.

[davedoesdev]

Yes:
elixir-lang/elixir#3268
elixir-lang/elixir#3517