update Z3 to latest version.
Z3 binary reports itself as `4.6.1.7785`,
but the files are named as `4.6.0-9-g36204fa`.
Z3 binary is compiled on Ubuntu 16.04 64bit,
according to the description in `java-smt/Developers.md`.
<!-- Solver Binaries -->
<dependency org="org.sosy_lab" name="javasmt-solver-mathsat" rev="5.5.0" conf="runtime-mathsat->solver-mathsat" />
- <dependency org="org.sosy_lab" name="javasmt-solver-z3" rev="z3-4.5.0-273-g899843b" conf="runtime-z3->solver-z3" />
+ <dependency org="org.sosy_lab" name="javasmt-solver-z3" rev="z3-4.6.0-9-g36204fa" conf="runtime-z3->solver-z3" />
<dependency org="org.sosy_lab" name="javasmt-solver-optimathsat" rev="1.4.0.10" conf="runtime-optimathsat->solver-optimathsat" />
<!-- Guava has a dependency on error_prone_annotations without a revision number, need an override. -->
