Forward compatibility with upcoming symfony/console v5 and current v4

This changeset includes a simple test to verify installation of this
project as dependency works alongside symfony/console:^4.0.

Symfony 5 has yet to be released (ETA this month), but some manual tests
against the current development version suggest this is supported as
well.

.travis.yml

@@ -19,6 +19,9 @@ matrix:
       dist: precise
     - php: 7.2
       script: composer build
+    - php: 7.2
+      install: []
+      script: composer install --dry-run --working-dir=tests/install-as-dep
   allow_failures:
     - php: hhvm
 

composer.json

@@ -5,11 +5,11 @@
     "homepage": "https://github.com/clue/graph-composer",
     "license": "MIT",
     "require": {
-        "php": "^5.3.6 || ^7.0",
+        "php": ">=5.3.6",
         "clue/graph": "^0.9.0",
         "graphp/graphviz": "^0.2.0",
         "jms/composer-deps-analyzer": "0.1.*",
-        "symfony/console": "^3.0 || ^2.1"
+        "symfony/console": "^5.0 || ^4.0 || ^3.0 || ^2.1"
     },
     "require-dev": {
         "clue/phar-composer": "^1.0",

src/Clue/GraphComposer/Command/Export.php

@@ -54,5 +54,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
         } else {
             readfile($path);
         }
+
+        return 0;
     }
 }

src/Clue/GraphComposer/Command/Show.php

@@ -25,5 +25,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
         $graph = new GraphComposer($input->getArgument('dir'));
         $graph->setFormat($input->getOption('format'));
         $graph->displayGraph();
+
+        return 0;
     }
 }

tests/install-as-dep/composer.json

@@ -0,0 +1,17 @@
+{
+    "require": {
+        "symfony/console": "^4.0"
+    },
+    "require-dev": {
+        "clue/graph-composer": "*@dev"
+    },
+    "repositories": [
+        {
+            "type": "path",
+            "url": "../../",
+            "options": {
+                "symlink": false
+            }
+        }
+    ]
+}