remove iOS target from pkg-config installation instructions as Homebr…

…ew does not support it

Signed-off-by: Rui Chen <[email protected]>

src/lib.rs

@@ -285,7 +285,7 @@ impl fmt::Display for Error {
                     io::ErrorKind::NotFound => {
                         let crate_name =
                             std::env::var("CARGO_PKG_NAME").unwrap_or_else(|_| "sys".to_owned());
-                        let instructions = if cfg!(target_os = "macos") || cfg!(target_os = "ios") {
+                        let instructions = if cfg!(target_os = "macos") {
                             "Try `brew install pkgconf` if you have Homebrew.\n"
                         } else if cfg!(unix) {
                             "Try `apt install pkg-config`, or `yum install pkg-config`,\n\