minor symfony#13179 Update frontend.rst (abdounikarim)

This PR was submitted for the 5.0 branch but it was merged into the 3.4 branch instead (closes symfony#13179).

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Update frontend.rst

fixing typo

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27ee711 Update frontend.rst

Author: javiereguiluz

frontend.rst

@@ -85,7 +85,7 @@ Issues & Questions
 Full API
 ........
 
-* `Full API`_: https://github.com/symfony/webpack-encore/blob/master/index.js
+* `Full API`_
 
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