Typo fix.

Author: rouilj

doc/rest.txt

@@ -1685,7 +1685,7 @@ You probably don't want to give this third party service your roundup
 username and credentials. Especially if your roundup instance is under
 your company's single sign on infrastructure.
 
-So what we need is a way for this third part service to impersonate
+So what we need is a way for this third party service to impersonate
 you and have access to create a roundup timelog entry (see
 `<customizing.html#adding-a-time-log-to-your-issues>`__ ). Then add it
 to the associated issue. This should happen without sharing passwords