Only expect a key on E-Mail-Verification when receiving a request (#434)

dj_rest_auth/registration/serializers.py

@@ -254,7 +254,7 @@ def save(self, request):
 
 
 class VerifyEmailSerializer(serializers.Serializer):
-    key = serializers.CharField()
+    key = serializers.CharField(write_only=True)
 
 
 class ResendEmailVerificationSerializer(serializers.Serializer):