fix version mismatch by changing footer to V5

[pcjentsch]

fixes #320

hopefully V5 is the correct version for both of these

With apache/arrow-rs#1631, files written by Arrow.jl are readable by arrow-rs.

[codecov-commenter]

Codecov Report

Merging #321 (16fc389) into main (bd872f4) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #321   +/-   ##
=======================================
  Coverage   87.15%   87.15%           
=======================================
  Files          26       26           
  Lines        3301     3301           
=======================================
  Hits         2877     2877           
  Misses        424      424           

Impacted Files	Coverage Δ
src/write.jl	96.63% <100.00%> (ø)

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[quinnj]

Thanks @pcjentsch!