Since Trump has only received about 37% of the primary vote, and a lot of those votes were not from Republicans but from Dems and independents in the open primaries, yes, by definition that makes Trump voters a minority in the GOP.
The daily caucus on FR suggests you are wrong...
Please - FR is not representative of the GOP at large.
If you want to restrict it to greater than 50% (one of many meanings of majority) no candidate has that and so the original premise by the OP is meaningless.
ma·jor·i·ty
noun: majority; plural noun: majorities
1. the greater number.
"in the majority of cases all will go smoothly" synonyms: larger part/number, greater part/number, best/better part