Fix references inside array and map

Added map and array cases to avro_refs.test.lua.

Rewritten avro_refs.test.lua to avoid nullable types in case of
avro-schema-2* (it does not work in many cases).

Thanks to Roman Proskin (@opomuc) for catching it up.

Author: Totktonada

graphql/avro_helpers.lua

@@ -225,12 +225,12 @@ function avro_helpers.expand_references(avro_schema, opts)
     elseif avro_t == 'array' or avro_t == 'array*' then
         local res = table.copy(avro_schema)
         res.items = avro_helpers.expand_references(avro_schema.items,
-            {definitons = definitions})
+            {definitions = definitions})
         return res
     elseif avro_t == 'map' or avro_t == 'map*' then
         local res = table.copy(avro_schema)
         res.values = avro_helpers.expand_references(avro_schema.values,
-            {definitons = definitions})
+            {definitions = definitions})
         return res
     elseif avro_helpers.is_scalar_type(avro_t) then
         return avro_schema