Update some docs from 2021-10 date triage (#1230)

Author: chansuke

src/backend/updating-llvm.md

@@ -67,7 +67,7 @@ Example PRs look like:
 ## Feature updates
 
 > Note that this information is as of the time of this writing <!-- date:
-2021-04 --> (April 2021). The process for updating LLVM changes with
+2021-10 --> (October 2021). The process for updating LLVM changes with
 practically all LLVM updates, so this may be out of date!
 
 Unlike bugfixes, updating to pick up a new feature of LLVM typically requires a

src/borrow_check/region_inference/member_constraints.md

@@ -94,7 +94,7 @@ member constraints come in.
 ## Choices are always lifetime parameters
 
 At present, the "choice" regions from a member constraint are always lifetime
-parameters from the current function. As of <!-- date: 2021-01 --> January 2021,
+parameters from the current function. As of <!-- date: 2021-10 --> October 2021,
 this falls out from the placement of impl Trait, though in the future it may not
 be the case. We take some advantage of this fact, as it simplifies the current
 code. In particular, we don't have to consider a case like `'0 member of ['1,