Give Error::text() a static lifetime

src/error.rs

@@ -28,12 +28,8 @@ impl Error {
         }
     }
 
-    pub fn text(&self) -> &str {
-        if let Some(description) = STR_ERROR.get(self.errno as usize) {
-            description
-        } else {
-            "Unknown Error"
-        }
+    pub fn text(&self) -> &'static str {
+        STR_ERROR.get(self.errno as usize).map(|&x| x).unwrap_or("Unknown Error")
     }
 }