Correct Composition.attester.mode sent as array (0..1 field in R4)

In FHIR R4, Composition.attester.mode is 0..1 (scalar code). In STU3 and
DSTU2 it's 0..* (array). Apply invariant sets a scalar string for R4.
STU3/DSTU2 keep the array form which is correct for those versions.

Author: kennethmyhra

lib/resource_generator.rb

@@ -440,7 +440,7 @@ def self.apply_invariants!(resource)
         when FHIR::CommunicationRequest
           resource.payload = nil
         when FHIR::Composition
-          resource.attester.each {|a| a.mode = ['professional']}
+          resource.attester.each {|a| a.mode = 'professional'}
           resource.section.each do |section|
             section.emptyReason = nil
             section.section.each do |sub|