Fix doc for escape_debug

[bombless]

No description provided.

[rust-highfive]

r? @aturon

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[steveklabnik]

@bors: delegate=kmcallister

[bors]

✌️ @kmcallister can now approve this pull request

[petrochenkov]

@bors r+ rollup

[bors]

📌 Commit a52f257 has been approved by petrochenkov

[bors]

⌛ Testing commit a52f257 with merge c7b058c...

[bors]

💔 Test failed - status-travis

[GuillaumeGomez]

Tests failure:

---- char::char::escape_debug_0 stdout ----
	error: use of unstable library feature 'char_escape_debug' (see issue #35068)
 --> <anon>:4:15
  |
4 | for i in '\n'.escape_debug() {
  |               ^^^^^^^^^^^^
  |
  = help: add #![feature(char_escape_debug)] to the crate attributes to enable

error: aborting due to previous error(s)

thread 'char::char::escape_debug_0' panicked at 'Box<Any>', /checkout/src/librustc/session/mod.rs:203
note: Run with `RUST_BACKTRACE=1` for a backtrace.

---- char::char::escape_debug_1 stdout ----
	error: use of unstable library feature 'char_escape_debug' (see issue #35068)
 --> <anon>:4:26
  |
4 | let quote: String = '\n'.escape_debug().collect();
  |                          ^^^^^^^^^^^^
  |
  = help: add #![feature(char_escape_debug)] to the crate attributes to enable

error: aborting due to previous error(s)

thread 'char::char::escape_debug_1' panicked at 'Box<Any>', /checkout/src/librustc/session/mod.rs:203

[GuillaumeGomez]

@bors: r-

[bors]

☔ The latest upstream changes (presumably #38909) made this pull request unmergeable. Please resolve the merge conflicts.

[clarfonthey]

This was bundled into #38909 so it's already merged.