clean up grammar on bug20307 changes file

pointed out by toralf on irc

changes/bug20307

@@ -1,7 +1,7 @@
   o Minor bugfixes (circuit, hidden service)
-    - When closing a circuit, the reason for doing so was assigned from a int
-      value to a uint16_t which is quite a problem for negative value that are
+    - When closing a circuit, the reason for doing so was assigned from an int
+      value to a uint16_t which is quite a problem for negative values that are
       our internal reasons (ex: END_CIRC_REASON_IP_NOW_REDUNDANT). On the HS
-      side, this was causing introduction point to be flagged as unusable
+      side, this was causing introduction points to be flagged as unusable
       because the reason wasn't the right one due to the bad conversion.
-      Partially fixes #21056 and fixes #20307; Bugfix on tor-0.2.8.1-alpha.
+      Partially fixes bug 21056 and fixes bug 20307; Bugfix on 0.2.8.1-alpha.