Support rust 1.51.0 (#789)

src/utils.rs

@@ -136,5 +136,9 @@ pub fn require<T: AsRef<OsStr> + Debug>(binary_name: T) -> Result<PathBuf> {
 
 #[allow(dead_code)]
 pub fn require_option<T>(option: Option<T>, cause: String) -> Result<T> {
-    option.ok_or_else(|| SkipStep(cause).into())
+    if let Some(value) = option {
+        Ok(value)
+    } else {
+        Err(SkipStep(cause).into())
+    }
 }