Fix inconsistency in tutorial.md

Text refers to "the type shown earlier", when the type in
question was not in fact shown earlier.  I assume this is
an artifact of an earlier revision.
auto merge of #11933 : kini/rust/patch-1, r=alexcrichton

Text refers to "the type shown earlier", when the type in
question was not in fact shown earlier.  I assume this is
an artifact of an earlier revision.