docs(readme): fix typo (#818)

README.md

@@ -84,7 +84,7 @@ This loader also supports the following loader-specific option:
 
 * `cacheCompression`: Default `true`. When set, each Babel transform output will be compressed with Gzip. If you want to opt-out of cache compression, set it to `false` -- your project may benefit from this if it transpiles thousands of files.
 
-* `customize`: Default `null`. The path of a module that exports a `custom` callback [like the one that you'd pass to `.custom()`](#customized-loader). Since you already have to make a new file to use this, it is recommended that you instead use `.custom` to create a wrapper loader. Only use this is you _must_ continue using `babel-loader` directly, but still want to customize.
+* `customize`: Default `null`. The path of a module that exports a `custom` callback [like the one that you'd pass to `.custom()`](#customized-loader). Since you already have to make a new file to use this, it is recommended that you instead use `.custom` to create a wrapper loader. Only use this if you _must_ continue using `babel-loader` directly, but still want to customize.
 
 ## Troubleshooting