Bug 1608753 - download the correct lucet package in bootstrap; r=emilio

We renamed the toolchain task in bug 1608428 and we forgot to update
bootstrap along with the renaming.

Differential Revision: https://phabricator.services.mozilla.com/D59699

--HG--
extra : moz-landing-system : lando

python/mozboot/mozboot/lucetc.py

@@ -4,4 +4,4 @@
 
 from __future__ import absolute_import, print_function, unicode_literals
 
-LINUX_LUCETC = 'lucetc'
+LINUX_LUCETC = 'linux64-lucetc'