inconsistency with enum type and value merge functions

[yaacovCR]

https://github.com/ardatan/graphql-tools/pull/2417/files#r554290366

[gmac]

From discussion concerning merge package enum tools:

It appears that the enum type and value mergers are implemented with reversed argument order from each other. While the enum type merger assigns A -> B, the enum value merger assigns B -> A. That means you'll end up with type settings from one candidate and value settings from the other.

Simple change but would require a major version bump for the fix.