Fix a broken heading

Author: bbatsov

FSharp-4.0/ListSeqArrayAdditions.md

@@ -14,7 +14,7 @@ Also, some functions were not defined on `Seq`, even though they exist in `List`
 
 The proposal below is to complete the matrix for `List`, `Array` and `Seq` w.r.t. functional collection functions.
 
-###Review and Completion
+### Review and Completion
 
 This work is only completed when all rows have a status of ":)". The library updates will only be done when all PRs are ready (or features are dropped).