Fix installation of gitshow/gitshowview completion symlinks

[twaugh]

Cherry-pick fix from #175 onto 0.4.x.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.60%. Comparing base (478d482) to head (622fb73).
⚠️ Report is 1 commits behind head on 0.4.x.

Additional details and impacted files

@@ Coverage Diff @@## 0.4.x #176 +/- ##
==========================================
- Coverage 86.24% 83.60% -2.64% 
==========================================
Files 15 5 -10 Lines 8527 4215 -4312 Branches 1854 1006 -848 ==========================================
- Hits 7354 3524 -3830 + Misses 1173 691 -482 

Flag	Coverage Δ
unittests	83.60% <ø> (-2.64%)	⬇️

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