Replace map in SpecHelpers::Sexp#sexp_find with inject
Replace map in SpecHelpers::Sexp#sexp_find with inject

For clearer indication of the method's recursion

JuliaCI/travis-build,JuliaCI/travis-build,akoeplinger/travis-build,jhass/travis-build,craigcitro/travis-build,akoeplinger/travis-build,kevmoo/travis-build,andyli/travis-build,craigcitro/travis-build,andyli/travis-build,jhass/travis-build,kevmoo/travis-build