Fix typo in a docstring

ligo/gracedb/rest.py

@@ -837,7 +837,7 @@ class GraceDb(GsiRest):
 
     @property
     def instruments(self):
-        """List of available instruments on ther server."""
+        """List of available instruments on the server."""
         return self.service_info.get('instruments')
 
     @property