min cpu shares is 2

src/apps.js

@@ -253,7 +253,7 @@ function validateMemoryLimit(manifest, memoryLimit) {
 function validateCpuShares(cpuShares) {
     assert.strictEqual(typeof cpuShares, 'number');
 
-    if (cpuShares <= 0 || cpuShares > 1024) return new BoxError(BoxError.BAD_FIELD, 'cpuShares has to be between 0 and 1024');
+    if (cpuShares < 2 || cpuShares > 1024) return new BoxError(BoxError.BAD_FIELD, 'cpuShares has to be between 2 and 1024');
 
     return null;
 }