Bump up rand dependency to 0.3.9

That's the first version with the correct getrandom syscall number for aarch64-unknown-linux-gnu.
servo · bors-servo · Jul 31, 2015 · Jul 31, 2015 · Jul 31, 2015 · b887445623d21af0b75a398cf84ff02f820d0c17
commit b887445623d21af0b75a398cf84ff02f820d0c17
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