Update versions

Z3 now moved to “master” based dev; so no need to mention stable
Ditto for ABC, I think the model there is to always use from the tip.

SMTSolverVersions.md

@@ -7,7 +7,6 @@ All testing was last done on Oct 5, 2015.
   * ABC:
       * https://bitbucket.org/alanmi/abc
       * Version 1.01
-      * Note: SMT-Lib support in ABC is fairly new. SBV uses the latest from the repo above.
   * Boolector:
       * http://fmv.jku.at/boolector/
       * Version 2.1.1
@@ -23,4 +22,3 @@ All testing was last done on Oct 5, 2015.
   * Z3:
       * https://github.com/Z3Prover/z3
       * Version 4.4.1
-      * Note: For floating-point logic, SBV uses the unstable-branch