content: fix typo in concurrency article
Reviewed-by: Daniel Martí <email@example.com>
diff --git a/content/concurrency.article b/content/concurrency.article
index 3d59db5..913c727 100644
@@ -1,5 +1,5 @@
-Go provides concurrency constructions as part of the core language. This lessons presents them and gives some examples on how to use it.
+Go provides concurrency constructions as part of the core language. This lesson presents them and gives some examples on how they can be used.
The Go Authors