Here's a few things that could be wrong:
1. Your mod id isn't "m1". In that case, change the "assets/m1" folder name accordingly.
2. Your item's registry name isn't "johncena". If it isn't, either change the model name or the registry name to match.
3. Your lang and/or model file could be formatted incorrectly. Post them here or on a service like pastebin so I can make sure they're correct.
And just a tip: the unlocalized name should be unique from any other mod. I'd reccomend changing it to "<modid>.johncena" to avoid conflicts with any other mod.
EDIT: Looking at this tutorial, it seems to use some old ways of registering items and models, the latter of which could be causing your model problem. For items, you should listen on the RegistryEvent.Register<Item> event (make a method with this type as a parameter, annotate the method with @EventSubscriber, and annotate the class with @Mod.EventBusSubscriber) and call "event.getRegistry().register(item)". Likewise, you should listen on the ModelRegistryEvent and use ModelLoader.setCustomModelResourceLocation instead of Minecraft.getMinecraft().getRenderItem()... for your item models. Also, the first parameter should just be "item.getRegistryName" instead of manually putting it together.