fix pyannotate annotations by changing relative paths to absolute paths

prepend_path_to_annotations.py

import json
from pathlib import Path

if __name__ == "__main__":
    dico = json.load(Path("./annotations.json").open())
    for element in dico:
        element["path"] = str(Path(__file__).parent) + "/" + element["path"]
    json.dump(dico, Path("./annotations_2.json").open("w"))

Very often I get "No files need to be modified" when the annotation files generated by pyannotate contains many annotations. This is probably related to my usage of pytest-annotate that does not mesh well with pyannotate. I don't know the root cause to be honest. This gist produce a file named annotations_2.json that have absolute paths in it, so that my pyannotate --type-info ./annotations_2.json --py3 -p -w . work at last.