Merge #1457

1457: Cargo.toml: Bump license-exprs to 1.4.0 r=carols10cents

And then update `Cargo.lock` with:

```console
$ cargo build
```

This bumps us from the SPDX License List 2.4 to 3.1.  Some 2.4 identifiers have since been deprecated by SPDX, but none of them have been removed, so it should be safe to deploy this before bumping Cargo and its docs (which mention 2.4 since rust-lang/cargo#4898).

Fixes #1278.

Author: bors-voyager[bot]

Cargo.lock

@@ -42,7 +42,7 @@ log = "0.3"
 env_logger = "0.5"
 hex = "0.3"
 htmlescape = "0.3.1"
-license-exprs = "^1.3"
+license-exprs = "^1.4"
 dotenv = "0.11.0"
 toml = "0.4"
 diesel = { version = "1.3.0", features = ["postgres", "serde_json", "chrono", "r2d2"] }