DOC: README: Fix broken link in migrator

A stray space in the link for the migrator repository wasn't allowing it
to be rendered properly in markdown viewers. Remove such a space to
avoid this.

Signed-off-by: Santiago Torres-Arias <torresariass@gmail.com>

README.md

@@ -76,8 +76,7 @@ may be the better choice.
 For those who have previously deployed their own registry based on the Registry
 1.0 implementation and wish to deploy a Registry 2.0 while retaining images,
 data migration is required. A tool to assist with migration efforts has been
-created. For more information see [docker/migrator]
-(https://github.com/docker/migrator).
+created. For more information see [docker/migrator](https://github.com/docker/migrator).
 ## Contribute