Update Dockerfile to rust 1.22, latest ImageMagick

Using latest bitflags crate requires a newer version of Rust.

cargo test passes

CHANGELOG.md

@@ -7,6 +7,7 @@ This file follows the convention described at
 
 ## [Unreleased]
 ### Changed
+- gentoo90: Hide more types from bindgen to fix the build for some systems
 - gentoo90: Build now supports Windows
 
 ## [0.7.0] - 2017-08-26

README.md

@@ -4,8 +4,8 @@ A somewhat safe Rust interface to the [ImageMagick](http://www.imagemagick.org/)
 
 ## Dependencies
 
-* Rust (~latest release) (on Windows you will require MSVC version)
+* Rust 1.20 or higher (on Windows you will require MSVC version)
-* Cargo (~latest release)
+* Cargo 0.20 or higher
 * ImageMagick (version 7.0.x)
     - Does _not_ work with ImageMagick 6.x due to backward incompatible changes.
     - [FreeBSD](https://www.freebsd.org): `sudo pkg install ImageMagick7`

docker/Dockerfile

@@ -1,10 +1,10 @@
-FROM rust:1.19.0-stretch
+FROM rust:1.22
 
 RUN apt-get update \
  && apt-get -y install curl build-essential clang pkg-config libjpeg-turbo-progs libpng-dev \
  && rm -rfv /var/lib/apt/lists/*
 
-ENV MAGICK_VERSION 7.0.7-14
+ENV MAGICK_VERSION 7.0.7-15
 
 RUN curl https://www.imagemagick.org/download/ImageMagick-${MAGICK_VERSION}.tar.gz | tar xz \
  && cd ImageMagick-${MAGICK_VERSION} \