I would suggest to use Lightroom's controls for fringing. From the looks of it, it looks like it should be on the "purple side" of blue, so heading into "Defringe" in "Lens Correction" and setting Purple Hue's selection to 0 on the lower end and being careful with the range you choose and the amount of defringing should mean you get rid of it but still keep the saturation of the sky.
Else, using the upper end of Green would be the next step.
These blue or purple tints are called chromatic aberration. They are caused when some lenses slightly split the wavelengths of light . Usually they are less in more expensive lenses. You can use colour fringing or lens correction tools to reduce these