Document return type for puppet 4.x functions

Author: lelutin

REFERENCE.md

@@ -308,7 +308,7 @@ data looked up in trocla
 The `trocla_gsub` replaces %%TROCLA_[\w_\-]+%% place holders with
 data looked up in trocla
 
-Returns: `Any`
+Returns: `String`
 
 ##### `data`
 
@@ -404,7 +404,7 @@ The `trocla_lookup_key` is a hiera 5 `lookup_key` data provider function.
 
 The `trocla_lookup_key` is a hiera 5 `lookup_key` data provider function.
 
-Returns: `Any`
+Returns: `String`
 
 ##### `key`
 

lib/puppet/functions/trocla/gsub.rb

@@ -7,6 +7,7 @@
   dispatch :trocla_gsub do
     param 'String', :data
     optional_param 'Struct[{ prefix => Optional[String] }]', :options
+    return_type 'String'
   end
 
   def trocla_gsub(data, options = {})

lib/puppet/functions/trocla_lookup_key.rb

@@ -16,6 +16,7 @@
     param 'Variant[String, Numeric]', :key
     param 'Hash', :options
     param 'Puppet::LookupContext', :context
+    return_type 'String'
   end
 
   def trocla_lookup_key(key, options, context)