Support for COMPOSER_BIN environment variable (#3)

 passing `COMPOSER_BIN` env variable instead

Co-authored-by: Thibaut Selingue <thibaut.selingue@lephare.com>

Author: cprn

bin/local-php-security-checker-installer

@@ -10,8 +10,10 @@ if (!isset($versionOutput[0])) {
 
 $version = $versionOutput[0];
 
+$composer = getenv('COMPOSER_BIN') ?: 'composer';
+
 $bindirOutput = null;
-exec('composer config bin-dir', $bindirOutput);
+exec("{$composer} config bin-dir", $bindirOutput);
 
 if (!isset($bindirOutput[0])) {
     exit(2);