Minor environment variables related bugfixes

Author: castarco

src/Installer/Installer.php

@@ -76,7 +76,7 @@ protected function executeComposerCommand($installPath)
 
         echo "\n";
         passthru(
-            $this->composerCmd.' --working-dir="'.$installPath.'" create-project dawehner/jupyter-php pkgs',
+            'PATH='.getenv('PATH').' '.$this->composerCmd.' --working-dir="'.$installPath.'" create-project dawehner/jupyter-php pkgs',
             $composerStatus
         );
         echo "\n";

src/System/UnixSystem.php

@@ -43,6 +43,7 @@ public function checkIfCommandExists($cmdName)
         }
 
         $sysResponse = exec(
+            'PATH='.getenv('PATH').'; '.
             "if command -v ".$cmdName." >/dev/null 2>&1; then echo \"true\"; else echo \"false\"; fi;"
         );