Conform fails to parse schema for umbrella app during release generation

Hi

I've been migrating my umbrella project to Erlang 20 and Elixir 1.5.0. I upgraded confrom from 2.1.2 to 2.5.0 to get latest fixes for Elixir 1.5.0 but now I have an error from conform plugin during release generation with distillery.

```
==> Assembling release..
==> Building release conform_umbrella_test:0.1.0 using environment dev
==> Plugin failed: Invalid schema at line 74: syntax error before: [<<"second_app.another_var">>].
```

I looked at the schema by dumping input argument for [`Conform.Schema.parse!/1`](https://github.com/bitwalker/conform/blob/master/lib/conform/schema.ex#L117) and got this in transform section:

```
transforms: [
"first_app.my_var": #Function<6.99386804/1 in :erl_eval.expr/5>,
"second_app.another_var": #Function<6.99386804/1 in :erl_eval.expr/5> # <-- line 74
],
```

Full schema from this step can be seen [here](https://github.com/tenkai9/conform_umbrella_test/blob/master/schema.exs).

I also checked non-umbrella app release generation and it works fine with similar case (using transforms). Instead of `inspect`ed anonymous functions in transform section (like in example above), there were actual functions text, which I assume is how it should be.

I've made a demo app which reproduces umbrella case https://github.com/tenkai9/conform_umbrella_test