Fix & on blocking reagents; make it symmetric

[tkf]

No description provided.

[tkf]

ref JuliaFolds/Transducers.jl#271 and JuliaFolds/Transducers.jl#40

[codecov]

Codecov Report

Merging #21 (f553a33) into master (0cec0c6) will increase coverage by 0.29%.
The diff coverage is 95.00%.

@@            Coverage Diff             @@
##           master      #21      +/-   ##
==========================================
+ Coverage   75.89%   76.19%   +0.29%     
==========================================
  Files          13       13              
  Lines         556      567      +11     
==========================================
+ Hits          422      432      +10     
- Misses        134      135       +1     

Flag	Coverage Δ
Pkg.test	76.19% <95.00%> (+0.29%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/combinators.jl	88.07% <94.44%> (+0.44%)	⬆️
src/refs.jl	91.11% <100.00%> (ø)
src/react.jl	76.54% <0.00%> (-0.29%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0cec0c6...f553a33. Read the comment docs.