Formatting fixes for endpoint provider

Author: Matt Muller

gems/smithy/lib/smithy/views/client/endpoint_provider.rb

@@ -116,7 +116,7 @@ def error_rule_with_condition(levels, rule)
         end
 
         def error(error, levels)
-          indent("raise ArgumentError, #{str(error)}", levels)
+          indent("raise ArgumentError, #{str(error)}\n", levels)
         end
 
         def tree_rule(rule, levels = 3)