Fix the problem with 0-arity functions without parens

We're now able to intercept these functions as expected.

CHANGELOG.md

@@ -1,6 +1,6 @@
 ## Known issues
 
-* intercepted functions without arguments that don't have `()` isn't working (e.g. `def foo, do: 123`)
+- None at this time :)
 
 # Changelog for v0.5.2
 

lib/configuration/configuration.ex

@@ -17,6 +17,11 @@ defmodule Interceptor.Configuration do
     get_interceptor_module_function_for(mfa_to_intercept, interception_type)
   end
 
+  def get_interceptor_module_function_for({module, function, nil = _arity} = to_intercept, interception_type) do
+    # functions with arity 0 without parens have their arity as nil
+    get_interceptor_module_function_for({module, function, 0}, interception_type)
+  end
+
   def get_interceptor_module_function_for({module, function, _arity} = to_intercept, interception_type) do
     interception_configuration = get_configuration(module)
     configuration = interception_configuration[to_intercept]

test/intercepted_modules/annotated/annotated_intercepted_on_before.ex

@@ -43,9 +43,8 @@ end
 defmodule AnnotatedInterceptedOnBefore4 do
   use Interceptor.Annotated
 
-  # TODO: Solve known issue 1
   @intercept true
-  def to_intercept(), do: "Hello, even without args"
+  def to_intercept, do: "Hello, even without args"
 
   @intercept true
   def bla, do: 123

test/intercepted_modules/do_block/intercepted_on_before.ex

@@ -42,8 +42,7 @@ defmodule InterceptedOnBefore4 do
   require Interceptor, as: I
 
   I.intercept do
-    # TODO: Solve known issue 1
-    def to_intercept(), do: "Hello, even without args"
+    def to_intercept, do: "Hello, even without args"
 
     def bla, do: 123
   end