Docker Build: Requirements.txt file

When I run the docker build command 

`docker build --build-arg city=diemen -t iens_scraper .`

I receive this error

```
Step 16/18 : RUN pip install -r requirements.txt
 ---> Running in fd6c80c23c4a
/bin/sh: 1: pip: not found
The command '/bin/sh -c pip install -r requirements.txt' returned a non-zero code: 127
```

Is there something I'm doing wrong?