bump required Rust version to 1.32

travis-ci pointed out that the dependency bump broke 1.31:

   Compiling docopt v1.1.0
error[E0658]: imports can only refer to extern crate names passed with `--extern` on stable channel (see issue #53130)
   --> /home/travis/.cargo/registry/src/github.com-1ecc6299db9ec823/docopt-1.1.0/src/parse.rs:48:5
    |
48  |   use regex;
    |       ^^^^^
    |

Looks like uniform_paths was stabilized in 1.32, and I verified locally that
version builds.

.travis.yml

@@ -23,7 +23,7 @@ matrix:
       script:
         - ci/script-rust.sh
     - language: rust
-      rust: 1.31.0
+      rust: 1.32.0
       script:
         - ci/script-rust.sh
     - language: node_js

guide/install-manual.md

@@ -45,7 +45,7 @@ all non-Rust dependencies:
                    pkgconf \
                    tzdata
 
-Next, you need Rust 1.31+ and Cargo. The easiest way to install them is by
+Next, you need Rust 1.32+ and Cargo. The easiest way to install them is by
 following the instructions at [rustup.rs](https://www.rustup.rs/).
 
 Finally, building the UI requires [yarn](https://yarnpkg.com/en/).

scripts/script-functions.sh

@@ -40,7 +40,7 @@ fi
 NODE_MIN_VERSION="8"
 YARN_MIN_VERSION="1.0"
 CARGO_MIN_VERSION="0.2"
-RUSTC_MIN_VERSION="1.31"
+RUSTC_MIN_VERSION="1.32"
 FFMPEG_MIN_VERSION="55.1.101"
 FFMPEG_RELEASE_VERSION="3.4"