Fix ERB deprecation warning (#360)

* Fix ERB deprecation warning

example warning:
```
lib/generators/scenic/model/model_generator.rb:39: warning: Passing safe_level with the 2nd argument of ERB.new is deprecated. Do not use it, and specify other arguments as keyword arguments.
```

followed Ruby standard library style to make distinction on ERB version check:
ruby/ruby@3406c5d

lib/generators/scenic/model/model_generator.rb

@@ -36,12 +36,23 @@ def invoke_view_generator
       def evaluate_template(source)
         source  = File.expand_path(find_in_source_paths(source.to_s))
         context = instance_eval("binding", __FILE__, __LINE__)
-        ERB.new(
-          ::File.binread(source),
-          nil,
-          "-",
-          "@output_buffer",
-        ).result(context)
+
+        if ERB.instance_method(:initialize).parameters.assoc(:key) # Ruby 2.6+
+          erb = ERB.new(
+            ::File.binread(source),
+            trim_mode: "-",
+            eoutvar: "@output_buffer",
+          )
+        else
+          erb = ERB.new(
+            ::File.binread(source),
+            nil,
+            "-",
+            "@output_buffer",
+          )
+        end
+
+        erb.result(context)
       end
 
       def generating?