Correctly highlight the behind glyph ⍛

**Information** - Language: APL - Plugins: none **Description** The new [Behind](https://aplwiki.com/wiki/Reverse_Compose) glyph is not highlighted correctly. **Code snippet** [Test page](https://prismjs.com/test.html#language=apl&text=3%C3%97%E2%8D%A8%E2%8D%9B-2%0A3%20%C2%AF1%204%C3%97%E2%8D%9B%C3%97%E2%88%98%7C%C2%AF2%20%C2%AF7%201) <details> <summary>⍛ should be highlighted the same as ⍨ and ∘</summary> ``` 3×⍨⍛-2 3 ¯1 4×⍛×∘|¯2 ¯7 1 ``` </details>