Update travis config to to use container infrastructure

.travis.yml

@@ -1,18 +1,13 @@
-sudo: required
+sudo: false
+
+cache: cargo
 
 install: |
-    mkdir -p ~/rust && \
     echo -e "\033[33;1mDownloading Rust\033[0m" && \
-    curl -sL https://static.rust-lang.org/dist/rust-nightly-$TARGET.tar.gz | tar --strip-components=1 -C ~/rust -xzf -
+    curl https://sh.rustup.rs -sSf | sh -s -- -y --default-toolchain nightly-$TARGET && \
+    export PATH=$HOME/.cargo/bin:$PATH
 
 before_script: |
-    sudo apt-get update && \
-    if [ $BITS -eq 32 ]; then \
-      sudo apt-get install libc6-dev:i386 libstdc++6:i386 zlib1g-dev:i386 libssl-dev:i386 pkg-config:i386 gcc-multilib libgmp-dev:i386; \
-    else \
-      sudo apt-get install libgmp-dev
-    fi && \
-    sudo ~/rust/install.sh
     pip install 'travis-cargo<0.2' --user && export PATH=$HOME/.local/bin:$PATH
     rustc --version
 
@@ -28,17 +23,40 @@ script:
 after_success:
     - if [ -z "$FEATURES" -a "$BITS" = "32" ]; then travis-cargo doc-upload; fi
 
+matrix:
+  include:
+    - env:
+      - TARGET=i686-unknown-linux-gnu
+        BITS=32
+        FEATURES=''
+      addons:
+        apt:
+          packages:
+          - libc6:i386
+          - libstdc++6:i386
+          - zlib1g-dev:i386
+          - libssl-dev:i386
+          - pkg-config:i386
+          - gcc-multilib
+          - libgmp-dev:i386
+    - env:
+      - TARGET=x86_64-unknown-linux-gnu
+        BITS=64
+        FEATURES=''
+      addons:
+        apt:
+          packages:
+          - libgmp-dev
+    - env:
+      - TARGET=x86_64-unknown-linux-gnu
+        BITS=64
+        FEATURES='asm'
+      addons:
+        apt:
+          packages:
+          - libgmp-dev
+
 env:
-  matrix:
-    - TARGET=i686-unknown-linux-gnu
-      BITS=32
-      FEATURES=''
-    - TARGET=x86_64-unknown-linux-gnu
-      BITS=64
-      FEATURES=''
-    - TARGET=x86_64-unknown-linux-gnu
-      BITS=64
-      FEATURES='asm'
   global:
     - TRAVIS_CARGO_NIGHTLY_FEATURE=unstable
     - secure: 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