doc: minor format fixes in book/error-handling

[lnmx]

No description provided.

[rust-highfive]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @brson (or someone else) soon.

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[steveklabnik]

@bors: r+ rollup

Thanks so much!

[bors]

📌 Commit 49dc357 has been approved by steveklabnik

[bors]

⌛ Testing commit 49dc357 with merge 524caf3...

[bors]

💔 Test failed - auto-win-gnu-32-opt

[alexcrichton]

@bors: retry

On Sun, Dec 20, 2015 at 3:10 AM, bors notifications@github.com wrote:

[image: 💔] Test failed - auto-win-gnu-32-opt
http://buildbot.rust-lang.org/builders/auto-win-gnu-32-opt/builds/2480

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Reply to this email directly or view it on GitHub
#30461 (comment).

[bors]

⌛ Testing commit 49dc357 with merge 1322e36...

[bors]

💔 Test failed - auto-win-gnu-64-opt

[alexcrichton]

@bors: retry

On Mon, Dec 21, 2015 at 3:02 AM, bors notifications@github.com wrote:

[image: 💔] Test failed - auto-win-gnu-64-opt
http://buildbot.rust-lang.org/builders/auto-win-gnu-64-opt/builds/2481

—
Reply to this email directly or view it on GitHub
#30461 (comment).

[alexcrichton]

@bors: retry