Fix test-child-process-cwd.js on Joyent servers

It's symlinked to /usr/bin so this test fails.

test/simple/test-child-process-cwd.js

@@ -30,7 +30,6 @@ function testCwd(options, forCode, forData) {
 }
 
 // Assume these exist, and 'pwd' gives us the right directory back
-testCwd( { cwd: '/bin'    }, 0, '/bin' );
 testCwd( { cwd: '/dev'    }, 0, '/dev' );
 testCwd( { cwd: '/'       }, 0, '/'    );
 
@@ -48,4 +47,4 @@ testCwd( { cwd: null      }, 0 );
 assert.notEqual(0, returns);
 process.addListener('exit', function () {
   assert.equal(0, returns);
-});
+});