replace obs/exp in hicAggregate with ones of those in hicexplorer

[LeilyR]

issue #758

Welcome to the HiCExplorer GitHub repository! Before opening the issue please check
that the following requirements are met :

• Search whether this issue (or a similar issue) has been solved before using the search tab above. Link the previous issue if appropriate below.

• Paste your HiCExplorer version (hicInfo --version) and your python version (python --version) below.

• Have you checked our documentation on hicexplorer.readthedocs.io?

• Do you use conda to install HiCExplorer?

• Do you use the latest HiCExplorer release? If not, please install it via a conda environment:
  conda create --name hicexplorer hicexplorer=3.6 python=3.8 -c bioconda -c conda-forge
  and activate the environment: conda activate hicexplorer. Retry your command. You can exit a conda environment via conda deactivate. To learn more about conda and environments, please consider the following documentation.

Retry your command, is it solved now? If not please continue with the following:

• Paste the full HiCExplorer command that produces the issue below
  (ignore if you simply spotted the issue in the code/documentation).

• Paste the output printed on screen from the command that produces the issue
  below (ignore if you simply spotted the issue in the code/documentation).