toolchain: Update to Rust 1.31.0

We updated the production toolchain from 1.30 to 1.31 in CL:1366446.
This CL does the same upgrade for the local developer toolchain and
Kokoro.

The relevant changes are in rust-toolchain and kokoro/Dockerfile.
The rest are from rustfmt.

TEST=cargo fmt --all -- --check
TEST=as described in kokoro/README.md

Change-Id: I3b4913f3e237baa36c664b4953be360c09efffd4
Reviewed-on: https://chromium-review.googlesource.com/1374376
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: David Tolnay <dtolnay@chromium.org>
Reviewed-by: Zach Reizner <zachr@chromium.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/plugin/mod.rs b/src/plugin/mod.rs
index 745fa4e..0aa2ff4 100644
--- a/src/plugin/mod.rs
+++ b/src/plugin/mod.rs
@@ -254,7 +254,8 @@ fn create_plugin_jail(root: &Path, seccomp_policy: &Path) -> Result<Minijail> {
         "tmpfs",
         (MS_NOSUID | MS_NODEV) as usize,
         "size=67108864",
-    ).map_err(Error::MountRoot)?;
+    )
+    .map_err(Error::MountRoot)?;
 
     Ok(j)
 }
@@ -439,7 +440,8 @@ pub fn run_vcpus(
                     vcpu_exit_evt
                         .write(1)
                         .expect("failed to signal vcpu exit eventfd");
-                }).map_err(Error::SpawnVcpu)?,
+                })
+                .map_err(Error::SpawnVcpu)?,
         );
     }
     Ok(())