unset fzf env variable when calling fzf

[KristofferC]

Fixes #236

cc @colinxs

[codecov-commenter]

Codecov Report

Merging #262 (9daf865) into master (573a9c7) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #262      +/-   ##
==========================================
- Coverage   19.47%   19.44%   -0.03%     
==========================================
  Files          12       12              
  Lines         868      869       +1     
==========================================
  Hits          169      169              
- Misses        699      700       +1     

Impacted Files	Coverage Δ
src/repl.jl	0.00% <0.00%> (ø)

---

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 573a9c7...9daf865. Read the comment docs.