Change language in competition script to smt2.6 (#171)

Change language in competition script to smt2.6 (#171)

* Change language in competition script to smt2.6

The benchmark scrambler for the application track cuts out
the :smt-lib-version command, so this commit sets it
manually to 2.6 (all benchmarks in SMT-COMP use the 2.6
standard) instead of 2.0. I have not seen any failures due
to that but might as well be prudent.

* Change language in competition script to smt2.6

The benchmark scrambler (at least for the application
track) cuts out the :smt-lib-version command, so this
commit sets it manually to 2.6 (all benchmarks in SMT-COMP
use the 2.6 standard) instead of 2.0. I have not seen any
failures due to that but might as well be prudent.