Fixing path for ContentBuilder project templates

Recent changes in MonoGame installation paths on Windows resulted in errors when creating ContentBuilder projects.

MonoGame.ContentPipeline.targets moved from "Program Files (x86)\MonoGame\v3.0" to "Program Files (x86)\MSBuild\MonoGame\v3.0"
MonoGameContentProcessors.dll as well.

I have checked the other templates and everything else seems to be fine.