fix(FutureWarnings): replace .append by pd.concat

[patrickleonardy]

Story Title

Update code to not raise any FutureWarnings

Changes made

• replaced df.append(new_row) by pd.concat([df, new_row)

How does the solution address the problem

We use the pd.concat method to do the same. see: Pandas docs

Linked issues

Resolves #190