chore: add Travis CI docs deployment job and update build dependencies

- Add automatic docs deployment stage for master branch pushes in .travis.yml
- Include python3-markdown, python3-pygments, python3-setuptools, and ruby-sass as build dependencies
- Switch from container-based to sudo-required builds with trusty dist for custom Pygments lexer installation
- Ensure build directory exists before generating docs in Makefile

src/optional/wren_opt_meta.c

@@ -61,9 +61,7 @@ void metaGetModuleVariables(WrenVM* vm)
   
   for (int i = 0; i < names->elements.count; i++)
   {
-    String* name = &module->variableNames.data[i];
-    names->elements.data[i] = wrenNewStringLength(vm,
-                                                  name->buffer, name->length);
+    names->elements.data[i] = OBJ_VAL(module->variableNames.data[i]);
   }
 }