Merge #1404

1404: Fight down failures! r=matklad a=mominul

issue #1400 

Now only `ra_tools` crate depends on `failure`, should I also fight those? 😁

Co-authored-by: Muhammad Mominul Huque <mominul2082@gmail.com>

crates/ra_project_model/src/sysroot.rs

@@ -38,18 +38,18 @@ impl Sysroot {
             .args(&["--print", "sysroot"])
             .output()?;
         if !rustc_output.status.success() {
-            failure::bail!("failed to locate sysroot")
+            Err("failed to locate sysroot")?
         }
         let stdout = String::from_utf8(rustc_output.stdout)?;
         let sysroot_path = Path::new(stdout.trim());
         let src = sysroot_path.join("lib/rustlib/src/rust/src");
         if !src.exists() {
-            failure::bail!(
+            Err(format!(
                 "can't load standard library from sysroot\n\
                  {:?}\n\
                  try running `rustup component add rust-src`",
                 src,
-            );
+            ))?;
         }
 
         let mut sysroot = Sysroot { crates: Arena::default() };