Your parents can certainly apply for a visa to visit you in the UK. Your impending job change should not affect their application, as @DumbCoder commented, and affirmed by @GayotFow. Your transition is the norm: you're currently employed, you'll work there until you move on to a new job, you'll be on probation initially.
As your question suggests that you are planning to sponsor your parents, be mindful that sponsorship does not mean that they don't have to show that they qualify on their own merits, they do.
@GayotFow, guru on UK Immigration, has noted:
[A]pplicants have often made the assumption that having a sponsor eliminates the need to demonstrate that they qualify. This is not true and, in many cases, needing a sponsor actually increases the onus on the applicant to demonstrate that they qualify.
The Immigration rules V 4.2 (e) require the applicant to...
... have sufficient funds to cover all reasonable costs in relation to their visit without working or accessing public funds. This includes the cost of the return or onward journey, any costs relating to dependants, and the cost of planned activities such as private medical treatment.
So it's not about the money and it doesn't matter how wealthy the sponsor is or how much money they are willing to commit; the onus never leaves the applicant to demonstrate that they qualify.
A sponsor's responsibility is to demonstrate the capacity to maintain and accommodate the application. Nothing else.