Fix endianness when reading the extra field of a gzip header

[Nemo157]

As specified in RFC1952 §2.1 multi-byte values are stored in little endian format.

Fixes #175

[Nemo157]

bors r+

[codecov-commenter]

Codecov Report

Base: 78.03% // Head: 78.36% // Increases project coverage by +0.33% 🎉

Coverage data is based on head (7118845) compared to base (7932607).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           prīmum     #176      +/-   ##
==========================================
+ Coverage   78.03%   78.36%   +0.33%     
==========================================
  Files          94       94              
  Lines        3068     3069       +1     
==========================================
+ Hits         2394     2405      +11     
+ Misses        674      664      -10     

Impacted Files	Coverage Δ
src/codec/gzip/header.rs	88.88% <100.00%> (+15.87%)	⬆️
tests/gzip.rs	100.00% <100.00%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

☔ View full report at Codecov.
📢 Do you have feedback about the report comment? Let us know in this issue.

[bors]

Build succeeded:

• cargo clippy
• cargo deny bans licenses sources
• cargo doc --cfg docsrs
• cargo fmt --check
• cargo hack check --all-targets --feature-powerset
• cargo hack check --feature-powerset
• cargo test
• cargo test --shallow-minimal-versions
• cargo test (stable, i686-pc-windows-msvc, windows-latest)
• cargo test (stable, i686-unknown-linux-gnu, ubuntu-latest)
• cargo test (stable, x86_64-apple-darwin, macos-latest)
• cargo test (stable, x86_64-pc-windows-msvc, windows-latest)
• cargo test (stable, x86_64-unknown-linux-gnu, ubuntu-latest)