Fix a typo in fd.rs. Fixes #30231.

[DiamondLovesYou]

Closes #30231

[rust-highfive]

r? @brson

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[alexcrichton]

@bors: r+ 3a6fd55

[bors]

⌛ Testing commit 3a6fd55 with merge 0f4e4df...

[bors]

💔 Test failed - auto-mac-64-opt

[alexcrichton]

@bors: retry

On Wednesday, December 9, 2015, bors notifications@github.com wrote:

[image: 💔] Test failed - auto-mac-64-opt
http://buildbot.rust-lang.org/builders/auto-mac-64-opt/builds/7332

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#30270 (comment).

[bors]

⚡ Previous build results for auto-linux-cross-opt, auto-linux-musl-64-opt, auto-win-msvc-32-opt are reusable. Rebuilding only auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-64-opt...

[bors]

💔 Test failed - auto-mac-64-opt

[alexcrichton]

@bors: retry

On Wed, Dec 9, 2015 at 10:06 AM, bors notifications@github.com wrote:

[image: 💔] Test failed - auto-mac-64-opt
http://buildbot.rust-lang.org/builders/auto-mac-64-opt/builds/7333

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#30270 (comment).

[bors]

⌛ Testing commit 3a6fd55 with merge 08a5b11...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, 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-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt