fourth attempt at travis config

* upgrade min required rust to 1.21; crossbeam-deque requires the
  ord_max_min feature, apparently stabilized in this version.

* use "make --jobs=2" to build ffmpeg so it goes faster.
  https://docs.travis-ci.com/user/reference/overview/ says there are 2
  cores available.

.travis.yml

@@ -4,7 +4,7 @@ language: rust
 rust:
   - stable
   - nightly
-  - 1.20.0
+  - 1.21.0
 addons:
   apt:
     packages:
@@ -20,7 +20,7 @@ matrix:
     - rust: nightly
 cache: cargo
 script:
-  - (git clone --depth 1 -b "release/3.4" https://github.com/FFmpeg/FFmpeg.git && cd FFmpeg && ./configure --enable-shared && make && sudo make install && sudo ldconfig)
+  - (git clone --depth 1 -b "release/3.4" https://github.com/FFmpeg/FFmpeg.git && cd FFmpeg && ./configure --enable-shared && make -jobs=2 && sudo make install --jobs=2 && sudo ldconfig)
   - cargo build --verbose --all
   - cargo test --verbose --all
   - 'if [ $TRAVIS_RUST_VERSION = nightly ]; then cargo bench --verbose --all; fi'

guide/install-manual.md

@@ -49,7 +49,7 @@ all non-Rust dependencies:
                    libssl-dev \
                    pkgconf
 
-Next, you need Rust 1.20+ and Cargo. The easiest way to install them is by
+Next, you need Rust 1.21+ 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="1.20"
+RUSTC_MIN_VERSION="1.21"
 FFMPEG_MIN_VERSION="55.1.101"
 FFMPEG_RELEASE_VERSION="3.4"