fix grammer

Author: haya14busa

doc/easymotion.txt

@@ -891,7 +891,7 @@ With this option enabled, |Easymotion| will shows target labels with
 uppercase letters, but allow you to type it in lowercase and have Easymotion
 automatically convert it uppercase.
 
-This feature improve targets' readability.
+This feature improves targets' readability.
 
 Example: >
 
@@ -1002,7 +1002,7 @@ EasyMotion_add_search_history                 *g:EasyMotion_add_search_history*
 EasyMotion_off_screen_search                   *g:EasyMotion_off_screen_search*
 
     If you set this option to 1, the 'n' key find motion will search patterns
-    even outside of the current screen range. If you want to disable this
+    even outside the current screen range. If you want to disable this
     feature, set this value to 0.
 >
     let g:EasyMotion_off_screen_search = 0