Also ignore cd output from stdout (#86)

In bash, `cd` will print the directory to stdout, so we also redirect
that output to /dev/null.

src/GraphQLSchemaLinter.php

@@ -79,7 +79,7 @@ public function getVersion() {
     if (!empty($this->dependencyVersions)) {
 
       foreach ($this->dependencyVersions as $name => $required) {
-        list($err, $dep_version, $stderr) = exec_manual('cd .arcanist 2>/dev/null && npm list --depth=0 2>/dev/null | grep "%C" | cut -d "@" -f 3 | tr -d "[:space:]"', $name);
+        list($err, $dep_version, $stderr) = exec_manual('cd .arcanist 2>&1 >/dev/null && npm list --depth=0 2>/dev/null | grep "%C" | cut -d "@" -f 3 | tr -d "[:space:]"', $name);
 
         if (empty($version) || !$this->checkVersion($dep_version, $required)) {
           $message = pht(