Make sure no error is output if env is missing

src/Composer/IO/ConsoleIO.php

@@ -162,6 +162,7 @@ class ConsoleIO implements IOInterface
             return $value;
         }
 
+        if (file_exists('/usr/bin/env')) {
             // handle other OSs with bash/zsh/ksh/csh if available to hide the answer
             $test = "/usr/bin/env %s -c 'echo OK' 2> /dev/null";
             foreach (array('bash', 'zsh', 'ksh', 'csh') as $sh) {
@@ -179,6 +180,7 @@ class ConsoleIO implements IOInterface
 
                 return $value;
             }
+        }
 
         // not able to hide the answer, proceed with normal question handling
         return $this->ask($question);