Moved Manifest.toml to gitignore

[timueh]

Since Pkg.jl is able to create Manifest.toml files automatically, CI runs a lot smoother when moving the Manifest.toml to the .gitignore.

[codecov-io]

Codecov Report

Merging #29 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #29   +/-   ##
=======================================
  Coverage   76.06%   76.06%           
=======================================
  Files          16       16           
  Lines         727      727           
=======================================
  Hits          553      553           
  Misses        174      174

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