added ErrorTypes for OerResponseError
Merge branch 'master' of github.com:snowplow/scala-forex

Conflicts:
	src/main/scala/com/snowplowanalytics/forex/Forex.scala
	src/main/scala/com/snowplowanalytics/forex/ForexClient.scala
	src/main/scala/com/snowplowanalytics/forex/oerclient/OerClient.scala
	src/test/scala/com/snowplowanalytics/forex/SpiedCacheSpecification.scala
	src/test/scala/com/snowplowanalytics/forex/TestHelper.scala
	src/test/scala/com/snowplowanalytics/forex/UnsupportedCurrencySpecification.scala