Update is-at-least 5.8.0.* calls for the release of zsh-5.8.1

[danielshahaf]

The following two checks:

zsh-syntax-highlighting/zsh-syntax-highlighting.zsh

Lines 159 to 166 in c10808a

	# The memo= feature was added to zsh in commit zsh-5.8-172-gdd6e702ee.
	# The version number at the time was 5.8.0.2-dev (see Config/version.mk).
	# Therefore, on 5.8.0.3 and newer the memo= feature is available.
	#
	# On zsh version 5.8.0.2 between the aforementioned commit and the
	# first Config/version.mk bump after it (which, at the time of writing,
	# is yet to come), this condition will false negative.
	if is-at-least 5.8.0.3 $ZSH_VERSION.0.0; then

zsh-syntax-highlighting/zsh-syntax-highlighting.zsh

Lines 416 to 418 in c10808a

	# See _zsh_highlight for the magic version number. (The use of 5.8.0.2
	# rather than 5.8.0.3 as in the _zsh_highlight is deliberate.)
	if is-at-least 5.8.0.2 $ZSH_VERSION.0.0 && _zsh_highlight__function_callable_p add-zle-hook-widget

were written when zsh-5.8 was the current release. zsh-5.8.1 has just been released as zsh-5.8 plus a handful of patches (none of which affect us). Those two conditions should be updated so they return false on zsh-5.8.1.

[danielshahaf]

If someone runs z-sy-h under zsh-5.8.1 (fairly likely to happen soon, since it's a security release), then both conditions would false positive.

---

The first condition would cause the memo feature to be used, which would be a problem:

zsh-syntax-highlighting/zsh-syntax-highlighting.zsh

Lines 176 to 182 in c10808a

	# Reset region_highlight to build it from scratch
	if (( zsh_highlight__memo_feature )); then
	region_highlight=( "${(@)region_highlight:#*memo=zsh-syntax-highlighting*}" )
	else
	# Legacy codepath. Not very interoperable with other plugins (issue #418).
	region_highlight=()
	fi

However, as the comment above the first condition explains, that condition is likely to only be evaluated at all during test suite runs, so this is less of a priority.

---

The second condition would enable the redrawhook codepath even though the memo feature isn't available. Per the comments above that condition, I assume this would reintroduce #579 and #735 for users of 5.8.1 until we fix this condition again.