Update Travis config to update Coveralls

This allows Coveralls to monitor the code coverage overtime and check
pull requests to ensure there is sufficient coverage.

.travis.yml

@@ -1,21 +1,57 @@
 language: rust
+cache: cargo
+
 rust:
   - stable
   - beta
-  - nightly
-before_script:
-  - rustup component add clippy
-  - rustup component add rustfmt
-jobs:
-  allow_failures:
-    - rust: nightly
-  fast_finish: true
+
 os:
   - linux
   - osx
   - windows
+
+before_script:
+  - rustup component add clippy
+  - rustup component add rustfmt
+
 script:
   - RUSTFLAGS="-D warnings" cargo build --verbose
   - cargo test --verbose
   - cargo clippy -- -D warnings
   - cargo fmt --all -- --check
+
+jobs:
+  fast_finish: true
+  allow_failures:
+    - rust: nightly
+  # The stable Linux build uploads results to Coveralls.
+  exclude:
+    - rust: stable
+      os: linux
+  include:
+    - rust: stable
+      os: linux
+      addons:
+        # Dependencies of kcov, used for cargo-travis.
+        apt:
+          packages:
+            - libcurl4-openssl-dev
+            - libelf-dev
+            - libdw-dev
+            - binutils-dev
+            - cmake
+          sources:
+            - kalakris-cmake
+      before_script:
+        - cargo install --force cargo-travis
+        - export PATH=$HOME/.cargo/bin:$PATH
+        - rustup component add clippy
+        - rustup component add rustfmt
+      after_success:
+        - cargo coveralls
+    # A basic check is done for the nightly version of Rust
+    - rust: nightly
+      os: linux
+      script:
+       - RUSTFLAGS="-D warnings" cargo build --verbose
+       - cargo test --verbose