pip-requirements.txt: Add Ecc required lib
    
    antlr4-python3-runtime is a lib to support Ecc run with Py3.x.
    
    Cc: Sean Brogan <sean.brogan@microsoft.com>
    Cc: Bret Barkelew <Bret.Barkelew@microsoft.com>
    Cc: Michael D Kinney <michael.d.kinney@intel.com>
    Cc: Liming Gao <liming.gao@intel.com>
    Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
    Reviewed-by: Liming Gao <liming.gao@intel.com>