docker: fix build, upgrade Go

[jsign]

The basic-miner-busybox Dockerfile is currently broken because of two issues.

Issue 1: missing jq dep now required to build extern/filecoin-ffi:

touch build/.update-modules
make -C extern/filecoin-ffi/ .install-filcrypto
make[1]: Entering directory '/lotus/extern/filecoin-ffi'
./install-filcrypto
+ auth_header=()
+ '[' -n '' ']'
++ dirname ./install-filcrypto
+ cd .
+ rust_sources_dir=rust
++ jq -r '.[].rustc_target_feature'
./install-filcrypto: line 23: jq: command not found
+ optimized_release_rustc_target_features=
make[1]: Leaving directory '/lotus/extern/filecoin-ffi'
make[1]: *** [Makefile:11: .install-filcrypto] Error 127
make: *** [Makefile:28: build/.filecoin-install] Error 2
The command '/bin/sh -c cd $SRC_DIR   && mkdir $SRC_DIR/build   && . $HOME/.cargo/env   && make clean   && make deps' returned a non-zero code: 2

Isse 2: failing extern/filecoin-ffi because of a “missing” C header file:

---> 90009b27540b
Step 18/40 : RUN cd $SRC_DIR   && . $HOME/.cargo/env   && make $MAKE_TARGET
 ---> Running in 704f07386d7e
rm -f lotus
go build -ldflags=-X="github.com/filecoin-project/lotus/build".CurrentCommit="+gitc9dae720.dirty" -o lotus ./cmd/lotus
# github.com/filecoin-project/filecoin-ffi/generated
extern/filecoin-ffi/generated/cgo_helpers.go:11:10: fatal error: cgo_helpers.h: No such file or directory
 #include "cgo_helpers.h"
          ^~~~~~~~~~~~~~~
compilation terminated.

This PR fixes both things making the Dockerfile build successfully.

[jsign]

Uhm, realized now that .dockerignore is a symlink to .gitignore... my original edit while doing the PR was editing .dockerignore, not .gitignore.

I don't like that symlink, since this change to .gitignore it isn't good. Also, might be a bit dangerous to think about doing a change on one file and really modify another one in a codebase. (Like happened now)

Maybe avoid the symlink? Or find other solution that still ignores .h but lets you build the Dockefile?
Opinions?

[placer14]

I proved the error existed and then proved the fix removed the error as described. Some further discussion about other improvement to be consider will follow in a separate PR.

Specifically:

• decouple .dockerignore from .gitignore
• optimize Dockerfile for caching and reduced git noise
• internalize extern depednencies within the docker image instead of COPYing from host

[placer14]

Nice catch on the duplicated install line.