Revert "Remove unused libc from Cargo.toml"

This reverts commit 0395368.

Author: Joshua Nelson

Cargo.toml

@@ -21,6 +21,7 @@ env_logger = "0.7"
 r2d2 = "0.8"
 r2d2_postgres = "0.14"
 url = "1.4"
+libc = "0.2"
 badge = { version = "0", path = "src/web/badge" }
 failure = "0.1.3"
 comrak = { version = "0.7", default-features = false }