Makefile: let target "micro-revision.i" be a prerequisite of the default target
Realized today, that a "make fuzzers" after a "make distclean" won't work due to
src/lib/version/git_revision.c:15:10: fatal error: micro-revision.i: No such file or directory
(tested at tor-0.4.0.1-alpha-98-g6c173d00f)