Fix typos and grammar mistakes pointed out by BitingBird.

debian/changelog

@@ -72,9 +72,9 @@ tails (1.3~rc1) unstable; urgency=medium
       environment variable. This will ease development and bug-fixing
       quite a bit.
     - Fix racy code in Tails Installer that sometimes made the
-      automated test suite stall when for scenarios installing Tails
+      automated test suite stall for scenarios installing Tails
       to USB disks. (Closes: #6092)
-    - Make it possible use Tails Upgrader to upgrade a Tails
+    - Make it possible to use Tails Upgrader to upgrade a Tails
       installation that has cruft files on the system partition.
       (Closes: #7678)
 
@@ -93,7 +93,7 @@ tails (1.3~rc1) unstable; urgency=medium
     - Hardcode the mirrors used at build and boot time in auto/config.
       Our stuff will be more consistent, easier to reproduce, and our
       QA process will be more reliable if we all use the same mirrors
-      at build time as the one we configure in the ISO. E.g. we won't
+      at build time as the ones we configure in the ISO. E.g. we won't
       have issues such as #8715 again. (Closes: #8726)
     - Don't attempt to retrieve source packages from local-packages so
       local packages can be installed via
@@ -136,7 +136,7 @@ tails (1.3~rc1) unstable; urgency=medium
     - Test that the Unsafe Browser:
       * starts in various locales.
       * complains when DNS isn't configured.
-      * tear down its chroot on shutdown.
+      * tears down its chroot on shutdown.
       * runs as the correct user.
       * has no plugins or add-ons installed.
       * has no unexpected bookmarks.