[DOC] Fix minor typo in signals.rdoc

Author: Stevo-S

doc/language/signals.rdoc

@@ -17,7 +17,7 @@ for its internal data structures, but it does not know when it is safe
 for data structures in YOUR code.  Ruby implements deferred signal
 handling by registering short C functions with only
 {async-signal-safe functions}[http://man7.org/linux/man-pages/man7/signal-safety.7.html] as
-signal handlers.  These short C functions only do enough tell the VM to
+signal handlers.  These short C functions only do enough to tell the VM to
 run callbacks registered via Signal.trap later in the main Ruby Thread.
 
 == Unsafe methods to call in Signal.trap blocks