changed pip command version

Dockerfile

@@ -4,6 +4,6 @@ RUN apt-get update -y
 RUN apt-get install -y python3-pip python3-dev build-essential
 COPY . /app
 WORKDIR /app
-RUN pip install -r requirements.txt
+RUN pip3 install -r requirements.txt
 ENTRYPOINT ["python3"]
 CMD ["app.py"]