Update pointer to Travis badge for 4.6.0.
Update pointer to Travis badge for 4.6.0.

Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java,Unidata/netcdf-java