minor #195 Fix controller classes docs (jmsche)

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Discussion
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Fix controller classes docs

Hi, just a little typo I added in the docs yesterday :)

Commits
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f12162a Fix controller classes docs

Author: weaverryan

README.md

@@ -243,7 +243,7 @@ If you want to set CSS classes:
 </div>
 
 <!-- or without values -->
-<div {{ stimulus_controller('chart', controllerClasses: { 'loading': 'spinner' }) }}>
+<div {{ stimulus_controller('chart', controllerClasses = { 'loading': 'spinner' }) }}>
     Hello
 </div>
 ```