Update src/avram/bulk_upsert.cr

Co-authored-by: Alex Piechowski <alex@piechowski.io>

Author: robcole

src/avram/bulk_upsert.cr

@@ -42,9 +42,9 @@ class Avram::BulkUpsert(T)
 
   private def fields
     @records.first.insert_values.keys.map do |key|
-      <<-TEXT
+      <<-SQL
       "#{key}"
-      TEXT
+      SQL
     end.join(", ")
   end