doc: Fix tutorial typo and remove unnecessary xfail-test

Author: cpeterso

doc/tutorial-tasks.md

@@ -220,7 +220,7 @@ let result = port.recv();
 The `Port` and `Chan` pair created by `stream` enables efficient communication
 between a single sender and a single receiver, but multiple senders cannot use
 a single `Chan`, and multiple receivers cannot use a single `Port`.  What if our
-example needed to computer multiple results across a number of tasks? The
+example needed to compute multiple results across a number of tasks? The
 following program is ill-typed:
 
 ~~~ {.xfail-test}

doc/tutorial.md

@@ -2393,7 +2393,7 @@ override the name used to search for the crate.
 
 Our example crate declared this set of `link` attributes:
 
-~~~~ {.xfail-test}
+~~~~
 #[link(name = "farm", vers = "2.5", author = "mjh")];
 ~~~~