Documentation: robust-futexes: fix spelling mistakes

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/robust-futexes.txt

@@ -126,9 +126,9 @@ vma based method:
 
  - no VM changes are needed - 'struct address_space' is left alone.
 
- - no registration of individual locks is needed: robust mutexes dont
+ - no registration of individual locks is needed: robust mutexes don't
    need any extra per-lock syscalls. Robust mutexes thus become a very
-   lightweight primitive - so they dont force the application designer
+   lightweight primitive - so they don't force the application designer
    to do a hard choice between performance and robustness - robust
    mutexes are just as fast.
 
@@ -202,7 +202,7 @@ and the remaining bits are for the TID.
 Testing, architecture support
 -----------------------------
 
-i've tested the new syscalls on x86 and x86_64, and have made sure the
+I've tested the new syscalls on x86 and x86_64, and have made sure the
 parsing of the userspace list is robust [ ;-) ] even if the list is
 deliberately corrupted.