Added new 64-bit architecture for Raspberry Pi 4

[robot-army]

I... don't think I've made many pull requests before, let me know if I've done this right!

It just changes one line in one file to try to make this work on a Raspberry Pi 4, but so far, it hasn't (at least not in local mode). It tends to fail like this:

[Build]   [main] Step 7/11 : RUN pip3 install aiohttp aiohttp_basicauth==0.1.3 aiortc==0.9.11 numpy==1.15.4 opencv-python==3.4.4.19 --index-url https://www.piwheels.org/simple
[Build]   [main]  ---> Running in be82c8861f50
[Build]   [main] Looking in indexes: https://www.piwheels.org/simple, https://www.piwheels.org/simple
[Build]   [main] Collecting aiohttp
[Build]   [main]   Downloading https://www.piwheels.org/simple/aiohttp/aiohttp-3.6.2-py3-none-any.whl (441kB)
[Build]   [main] Collecting aiohttp_basicauth==0.1.3
[Build]   [main]   Downloading https://www.piwheels.org/simple/aiohttp-basicauth/aiohttp_basicauth-0.1.3-py3-none-any.whl
[Build]   [main] ERROR: Could not find a version that satisfies the requirement aiortc==0.9.11 (from versions: none)
[Build]   
[Build]   [main] ERROR: No matching distribution found for aiortc==0.9.11
[Build]   
[Build]   [main] Removing intermediate container be82c8861f50
Some services failed to build:
    main: The command '/bin/sh -c pip3 install aiohttp aiohttp_basicauth==0.1.3 aiortc==0.9.11 numpy==1.15.4 opencv-python==3.4.4.19 --index-url https://www.piwheels.org/simple' returned a non-zero code: 1

[mbalamat]

@robot-army can you rebase on the current master and change your commit, by copying the current dockerfile and use the same first line as your current commit?

[mbalamat]

@robot-army thanks for your contribution I'll merge #67 which has your commit, and close this PR. Thanks again!