Merge pull request ruby-concurrency#648 from meineerde/patch-1

Fix code comment in Concurrent::Array

lib/concurrent/array.rb

@@ -15,7 +15,7 @@ module Concurrent
     #
     #   @note `a += b` is **not** a **thread-safe** operation on
     #   `Concurrent::Array`. It reads array `a`, then it creates new `Concurrent::Array`
-    #   which is concatenation of `a` and `b`, then it writes the concatenation to `b`.
+    #   which is concatenation of `a` and `b`, then it writes the concatenation to `a`.
     #   The read and write are independent operations they do not form a single atomic
     #   operation therefore when two `+=` operations are executed concurrently updates
     #   may be lost. Use `#concat` instead.