Update dependencies, Pico now requires PHP 7.0.8+

Pico now depends on Twig 2.12, Symfony YAML 3.4, Parsedown 1.7.4 and Parsedown Extra 0.8.1.

composer.json

@@ -31,11 +31,11 @@
         "source": "https://github.com/picocms/Pico"
     },
     "require": {
-        "php": ">=5.3.6",
-        "twig/twig": "^1.36",
-        "symfony/yaml" : "^2.8",
-        "erusev/parsedown": "1.8.0-beta-7",
-        "erusev/parsedown-extra": "0.8.0-beta-1"
+        "php": "^7.0.8",
+        "twig/twig": "^2.12",
+        "symfony/yaml" : "^3.4",
+        "erusev/parsedown": "1.7.4",
+        "erusev/parsedown-extra": "0.8.1"
     },
     "suggest": {
         "picocms/pico-theme": "Pico requires a theme to actually display the contents of your website. This is Pico's official default theme.",

index.php.dist

@@ -11,8 +11,8 @@
  */
 
 // check PHP platform requirements
-if (PHP_VERSION_ID < 50306) {
-    die('Pico requires PHP 5.3.6 or above to run');
+if (PHP_VERSION_ID < 70008) {
+    die('Pico requires PHP 7.0.8 or above to run');
 }
 if (!extension_loaded('dom')) {
     die("Pico requires the PHP extension 'dom' to run");