replace "ps comm" with "ps" in the function listPidsByComm

There exists an incompatibility problem as the shell command "ps comm" is invalid in some devices such as Google Pixel.

Below is the output when I issued "ps com" in Pixel:

 1|sailfish:/ $ ps com
 bad pid 'com'
 1|sailfish:/ $ echo $?
 1

So I replaced "ps comm" with "ps" which is workable for all the Android device.

lib/util/devutil.js

@@ -39,7 +39,7 @@ devutil.listPidsByComm = function(adb, serial, comm, bin) {
     shell: true
   }
 
-  return adb.shell(serial, ['ps', comm])
+  return adb.shell(serial, ['ps'])
     .then(function(out) {
       return new Promise(function(resolve) {
         var header = true