runtime: fix for implementation notes appearing in godoc

Change-Id: I31cfae1e98313b68e3bc8f49079491d2725a662b
Reviewed-on: https://go-review.googlesource.com/38850Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/mgclarge.go

@@ -24,7 +24,7 @@
 // removeSpan: which removes a specific span from the treap
 //
 // _mheap.lock must be held when manipulating this data structure.
-//
+
 package runtime
 
 import (