Fix a malformed if statement in the function rvm

The rvm function does not execute "rvm reload" when the new directory
contains a .ruby-version file, because the malformed if statement just
looks for a .rvmrc file.

Fish's syntax for if statements with several conditions is the following:
  if begin; CONDITION1; [and|or] CONDITION2; ...; end
rather than:
  if CONDITION1; [and|or] CONDITION2; ...