try! -> ?

Automated conversion using the untry tool [1] and the following command:

```
$ find -name '*.rs' -type f | xargs untry
```

at the root of the Rust repo.

[1]: https://github.com/japaric/untry

src/librustdoc/html/toc.rs

@@ -183,15 +183,15 @@ impl fmt::Debug for Toc {
 
 impl fmt::Display for Toc {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        try!(write!(fmt, "<ul>"));
+        write!(fmt, "<ul>")?;
         for entry in &self.entries {
             // recursively format this table of contents (the
             // `{children}` is the key).
-            try!(write!(fmt,
+            write!(fmt,
                         "\n<li><a href=\"#{id}\">{num} {name}</a>{children}</li>",
                         id = entry.id,
                         num = entry.sec_number, name = entry.name,
-                        children = entry.children))
+                        children = entry.children)?
         }
         write!(fmt, "</ul>")
     }