Update underscore.array.selectors.js.md

Author: dbwhddn10

docs/underscore.array.selectors.js.md

@@ -84,7 +84,7 @@ If wrapping a function around `_.nth` is too tedious or you'd like to partially
 
 #### partitionBy
 
-**Signature:** `_.keep(array:Array, fun:Function)`
+**Signature:** `_.partitionBy(array:Array, fun:Function)`
 
 Takes an array and partitions it into sub-arrays as the given predicate changes
 truth sense.
@@ -162,4 +162,4 @@ _.third(_.range(10), 5)
 //=> [2, 3, 4]
 ```
 
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