I actually used serebii's dex to check a while ago, it's very easy to use when looking for things like this, simply search by type. Here's a link if you need it:
http://serebii.net/pokedex-dp/
I can't find a case of a Pokemon's primary typing changing, because like blasphemy stated, the primary typing is the "defining" characteristic of a Pokemon, and doesn't change by evolution (unlike secondary typing). A few examples:
Skorupi (Poison/Bug) -> Drapion (Poison/Dark)
Mudkip (Water) -> Marshtomp (Water/Ground)
Surskit (Bug/Water) -> Masqurain (Bug/Flying)
EDIT: One thing I realized (unfortunately) looking at the rumor again: The rumored typing #639 Ground/Bug can't be the Pinsir evo we want because of the Primary type... but it's important to remember these are just rumors: the person who created them may have just mixed up the order of the types, so we can't rule out anything!