Run `apt-get update` before the build on Travis CI
Install lapack before the build on Travis CI

The [libsundials-serial-dev](http://packages.ubuntu.com/precise/libsundials-serial-dev)
package in the Ubuntu version installed on Travis CI has a missing dependency on
[liblapack-dev](http://packages.ubuntu.com/precise/liblapack-dev). Install
it before the build.