Corrected the spelling by separating the two words "to" & "prepend" in Q4 under collections.md

Author: keithmchd48

challenges/collections.md

@@ -142,7 +142,7 @@ To remove the elements from the end of the array `pop` operation can be used but
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 #### Q4
-### Write a program toprepend a single or multiple values in to an array
+### Write a program to prepend a single or multiple values in to an array
 
 - Values to the array can be prepended using `unshift` method of array