Strengthened Inhibitory Connections Between Neurons
The learning rule you describe (i.e. the change of synaptic weights from source neuron to target neuron depending on the temporal difference between source and target activity) is often referred to as 'classical' or 'standard' STDP (spike-timing dependent plasticity) and is focused on connections between excitatory cells. However, this simple form of plasticity is not enough to explain all experimental observations and has also computational problems with respect to stability i.e. there is in fact no 'standard' STDP, because the weight change is not only dependent on the temporal difference, but also on the voltage, location of the synapse, firing rate, the cell-type and probably other factors, see e.g. this article from 2010 dealing with questions surrounding STDP by Lisman and Spruston.

In short, the form of the learning rule depends on several factors and synaptic plasticity works differently for inhibitory cells. 
As the question as to how plasticity works involving inhibitory cells is not an easy topic, I will refer to this review paper which deals with different induction protocols and potential functional implications (e.g. stability, homeostasis): 
Review paper on inhibitory synaptic plasticity by Vogels et al.

Very recently, there also has been a research topic in Frontiers of Cellular Neuroscience on this topic: The editorial article briefly summarizes the different contributions