Drop codegen unit count to reduce final binary size.

 File  .text     Size Crate
 4.4%  12.8% 377.0KiB std
 3.6%  10.4% 306.8KiB reqwest
 2.6%   7.4% 217.4KiB regex
 2.5%   7.1% 209.5KiB clap
 2.5%   7.1% 208.2KiB [Unknown]
 2.2%   6.2% 183.8KiB regex_syntax
 2.1%   5.9% 175.4KiB rustls
 1.7%   4.9% 146.1KiB goblin
 1.2%   3.5% 102.9KiB object
 1.2%   3.4% 100.4KiB libgit2_sys
 1.0%   2.8%  83.8KiB ring
 1.0%   2.7%  81.0KiB backtrace
 1.0%   2.7%  80.7KiB unicode_normalization
 0.9%   2.5%  73.0KiB git_req
 0.7%   2.1%  61.8KiB h2
 0.7%   1.9%  56.3KiB yaml_rust
 0.5%   1.4%  42.2KiB hyper
 0.5%   1.3%  39.3KiB http
 0.4%   1.2%  35.0KiB duct
 0.4%   1.1%  33.9KiB term

Author: arusahni

Cargo.toml

@@ -16,6 +16,7 @@ build = "build.rs"
 [profile.release]
 lto = true
 opt-level = "s"
+codegen-units = 1
 
 [badges]
 travis-ci = { repository = "arusahni/git-req" }