Really depends on how much you can spend on your laptop, i3 (dual-core) with 4-8gb RAM is enough. but if you really can spend more than that, get an i5 or even i7. The important thing here is support for virtualization which is supported by all the CPUs these days (virtualization because you might have to run a virtual machine, it helps.. not really necessary but helps.)

so, i3 is enough and 4 to 8 gb ram is cool. good luck! :)