docs: fix macos install guide

[foray1010]

--with-lldb --with-toolchain are removed from https://github.com/Homebrew/homebrew-core/blob/master/Formula/llvm.rb

[codecov-commenter]

Codecov Report

Merging #373 into master will decrease coverage by 0.54%. The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #373      +/-   ##
==========================================
- Coverage   79.53%   78.98%   -0.55%     
==========================================
  Files          33       33              
  Lines        4744     4744              
==========================================
- Hits         3773     3747      -26     
- Misses        971      997      +26     

Impacted Files	Coverage Δ
src/llv8.cc	71.71% <0.00%> (-2.29%)	:arrow_down:
src/llv8.h	81.81% <0.00%> (-2.28%)	:arrow_down:
src/llv8-constants.h	97.05% <0.00%> (-1.48%)	:arrow_down:
src/llv8-inl.h	90.42% <0.00%> (-0.82%)	:arrow_down:
src/llv8-constants.cc	85.92% <0.00%> (-0.76%)	:arrow_down:

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