Test description typo in PriorityQueue.test.js

[iamlockon]

As title, it appears to me that the test description in line 37 :

 it('should be possible to change priority of internal nodes', () => {

and in line 54 :

 it('should be possible to change priority of head node', () => {

should be exchanged, since the node with item of value '100' should be the head node in my opinion. Thank you.

[trekhleb]

@iamlockon I guess you're right. The naming should be fixed now.