Fix markdown formatting error of E0277, E0310 and E0502.

[kennytm]

Fix bad format we see in https://doc.rust-lang.org/nightly/error-index.html#E0277.

[rust-highfive]

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

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[GuillaumeGomez]

Thanks!

@bors: r+ rollup

[bors]

📌 Commit 34bcc3d has been approved by GuillaumeGomez

[bors]

⌛ Testing commit 34bcc3d with merge d5d0521...

[bors]

💔 Test failed - auto-linux-64-opt-rustbuild

[kennytm]

@GuillaumeGomez Should have fixed test failure in ae75593 due to E0284 also wrongly formatted. (I think I don't have permission to ask @bors to retry 😄)

[GuillaumeGomez]

You don't, indeed.

@bors: r+ rollup

[bors]

📌 Commit ae75593 has been approved by GuillaumeGomez

[bors]

⌛ Testing commit ae75593 with merge b1b7526...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-32cross-opt, auto-linux-64-cargotest, auto-linux-64-cross-armhf, auto-linux-64-cross-armsf, auto-linux-64-cross-freebsd, auto-linux-64-cross-netbsd, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-opt-mir, auto-linux-64-opt-rustbuild, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-mac-64-opt-rustbuild, auto-mac-cross-ios-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-32-opt-rustbuild, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-cross-opt, auto-win-msvc-32-opt, auto-win-msvc-64-cargotest, auto-win-msvc-64-opt, auto-win-msvc-64-opt-mir, auto-win-msvc-64-opt-rustbuild