Fix nim version requirements in .nimble

v0.3.4

notable fixes:
- refactor: remove shallowCopy
- avoid nzCompressInit ambiguous call when included (#80)
- make getUnderlyingType work with type argument (#83)

disable vcc compiler test

Merge pull request #50 from jangko/bump_version

bump version to 0.3.1

Merge pull request #47 from jangko/apidoc

update apidoc.md

Merge pull request #45 from jangko/fuzzing

more robust PNG loader, fuzz tested

Merge pull request #41 from jangko/fix_readme

fix appveyor badge

Merge pull request #34 from jangko/nim_1.0

compile with Nim 1.0.0