Update installation.rst

Minor grammar correction

Author: ericpoe

book/installation.rst

@@ -69,7 +69,7 @@ Distribution:
     To download the vendor files faster, add the ``--prefer-dist`` option at
     the end of any Composer command.
 
-This command may take several minutes to run as Composer download the Standard
+This command may take several minutes to run as Composer downloads the Standard
 Distribution along with all of the vendor libraries that it needs. When it finishes,
 you should have a directory that looks something like this: