Drop support for HHVM and PHP 5.6

Also make some improvements on .travis.yml file.

.travis.yml

@@ -1,29 +1,33 @@
-sudo:
-  false
+sudo: false
 
-language:
-  php
+language: php
 
-php:
-  - 5.6
-  - 7.0
-  - 7.1
-  - hhvm
+cache:
+  directories:
+    - $HOME/.composer/cache
+
+matrix:
+  include:
+    - php: 7.0
+    - php: 7.1
+    - php: nightly
+  allow_failures:
+    - php: nightly
+  fast_finish: true
 
 before_script:
-  - composer self-update
-  - composer install --no-interaction --prefer-source
+  - composer install --prefer-dist
 
 script:
   - vendor/bin/phpunit --configuration phpunit.xml.dist --colors --coverage-clover=coverage.clover
-  - vendor/bin/docheader check library tests
+  - |
+    if [[ "${TRAVIS_PHP_VERSION}" == "7.0" ]]; then
+      vendor/bin/docheader check library tests
+    fi
 
 after_script:
-  - test "5.6" == "${TRAVIS_PHP_VERSION}" && wget https://scrutinizer-ci.com/ocular.phar
-  - test -f ocular.phar && php ocular.phar code-coverage:upload --format=php-clover coverage.clover
-
-notifications:
-  irc:
-    channels:
-      - "irc.freenode.org#php-respect"
-    use_notice: true
+  - |
+    if [[ "${TRAVIS_PHP_VERSION}" == "7.0" ]]; then
+      wget https://scrutinizer-ci.com/ocular.phar
+      php ocular.phar code-coverage:upload --format=php-clover coverage.clover
+    fi

README.md

@@ -13,7 +13,7 @@
 - [Granularity control](docs/README.md#validation-methods) for advanced reporting.
 - More than 100 (fully tested) validators.
 - [A concrete API](docs/CONCRETE_API.md) for non fluent usage.
-- Works on PHP 5.6+ or HHVM 3.6+
+- Works on PHP 5.6+
 
 ## Table of contents
 

composer.json

@@ -12,7 +12,7 @@
         }
     ],
     "require": {
-        "php": ">=5.6",
+        "php": ">=7.0",
         "symfony/polyfill-mbstring": "^1.2"
     },
     "require-dev": {