Fix a typo in the example of using if inside select macro.

src/part-guide/concurrency-primitives.md

@@ -81,7 +81,7 @@ You'll notice things are already more interesting than with the `join` macro bec
 Tokio's `select` macro supports a bunch of features:
 
 - pattern matching: the syntax on the left of `=` on each branch can be a pattern and the block is only executed if the result of the future matches the pattern. If the pattern does not match, then the future is no longer polled (but other futures are). This can be useful for futures which optionally return a value, e.g., `Some(x) = do_a_thing() => { ... }`.
-- `if` guards: each branch may have an `if` guard. When the `select` macro runs, after evaluating each expression to produce a future, the `if` guard is evaluated and the future is only polled if the guard is true. E.g., `x = = do_a_thing() if false => { ... }` will never be polled. Note that the `if` guard is not re-evaluated during polling, only when the macro is initialized.
+- `if` guards: each branch may have an `if` guard. When the `select` macro runs, after evaluating each expression to produce a future, the `if` guard is evaluated and the future is only polled if the guard is true. E.g., `x = do_a_thing(), if false => { ... }` will never be polled. Note that the `if` guard is not re-evaluated during polling, only when the macro is initialized.
 - `else` branch: `select` can have an `else` branch `else => { ... }`, this is executed if all the futures have stopped and none of the blocks have been executed. If this happens without an `else` branch, then `select` will panic.
 
 The value of the `select!` macro is the value of the executed branch (just like `match`), so all branches must have the same type. E.g., if we wanted to use the result of the above example outside of the `select`, we'd write it like