bump required rust to 1.27

1.26 doesn't work with the updated rusqlite:

error[E0658]: use of unstable library feature 'duration_extras' (see issue #46507)
  --> /home/travis/.cargo/registry/src/github.com-1ecc6299db9ec823/rusqlite-0.14.0/src/busy.rs:26:49
   |
26 |             .and_then(|t| t.checked_add(timeout.subsec_millis().into()))
   |                                                 ^^^^^^^^^^^^^

.travis.yml

@@ -4,7 +4,7 @@ language: rust
 rust:
   - stable
   - nightly
-  - 1.26.0
+  - 1.27.0
 addons:
   apt:
     packages:

guide/install-manual.md

@@ -44,7 +44,7 @@ all non-Rust dependencies:
                    libssl-dev \
                    pkgconf
 
-Next, you need Rust 1.26+ and Cargo. The easiest way to install them is by
+Next, you need Rust 1.27+ 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="1.26"
+RUSTC_MIN_VERSION="1.27"
 FFMPEG_MIN_VERSION="55.1.101"
 FFMPEG_RELEASE_VERSION="3.4"