link needs puncuation

Author: davidszotten

src/doc/trpl/error-handling.md

@@ -28,7 +28,7 @@ systems may want to jump around.
     * [The `Result` type](#the-result-type)
         * [Parsing integers](#parsing-integers)
         * [The `Result` type alias idiom](#the-result-type-alias-idiom)
-    * [A brief interlude: unwrapping isn't evil](#a-brief-interlude-unwrapping-isnt-evil)
+    * [A brief interlude: unwrapping isn't evil](#a-brief-interlude:-unwrapping-isn't-evil)
 * [Working with multiple error types](#working-with-multiple-error-types)
     * [Composing `Option` and `Result`](#composing-option-and-result)
     * [The limits of combinators](#the-limits-of-combinators)
@@ -41,7 +41,7 @@ systems may want to jump around.
     * [The real `try!` macro](#the-real-try!-macro)
     * [Composing custom error types](#composing-custom-error-types)
     * [Advice for library writers](#advice-for-library-writers)
-* [Case study: A program to read population data](#case-study-a-program-to-read-population-data)
+* [Case study: A program to read population data](#case-study:-a-program-to-read-population-data)
     * [Initial setup](#initial-setup)
     * [Argument parsing](#argument-parsing)
     * [Writing the logic](#writing-the-logic)