datasette publish now is broken in master

[simonw]

>     gcc -pthread -Wno-unused-result -Wsign-compare -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -fPIC -I/usr/local/include/python3.6m -c httptools/parser/parser.c -o build/temp.linux-x86_64-3.6/httptools/parser/parser.o -O2
>     unable to execute 'gcc': No such file or directory
>     error: command 'gcc' failed with exit status 1
>     
>     ----------------------------------------
> Command "/usr/local/bin/python -u -c "import setuptools, tokenize;__file__='/tmp/pip-install-s73273rj/httptools/setup.py';f=getattr(tokenize, 'open', open)(__file__);code=f.read().replace('\r\n', '\n');f.close();exec(compile(code, __file__, 'exec'))" install --record /tmp/pip-record-yha7dxqq/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /tmp/pip-install-s73273rj/httptools/

Turns out the python-slim base image I introduced in b18e451 doesn't include gcc: docker-library/python#60 (comment)