Upgrade rust-block to silence warning

SSheldon/rust-block#1 Relevant to #7513
servo · bors-servo · Sep 3, 2015 · Sep 3, 2015 · Sep 3, 2015 · 68e65d775a470655c302fcd9d049bed450bb5b68
commit 68e65d775a470655c302fcd9d049bed450bb5b68
diff --git a/components/servo/Cargo.lock b/components/servo/Cargo.lock
diff --git a/ports/cef/Cargo.lock b/ports/cef/Cargo.lock
diff --git a/ports/gonk/Cargo.lock b/ports/gonk/Cargo.lock