43651-type-parameters.md: add missing backquote
43651-type-parameters.md: add missing backquote

Change-Id: If29e34707f08d9418ae96e1b15badc1a1b84abcd
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/348709
Trust: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/proposal,golang/proposal