add sed -i lint check to ensure portability

ci/lint.sh

@@ -5,5 +5,10 @@ if [ -x "$(command -v shellcheck)" ]; then
 else
 	echo "Warning: shellcheck is not installed, skipping shell scripts"
 fi
+incompatible_sed=$(! grep -RPn --color=always --exclude-dir=node_modules --exclude-dir=.git 'sed(?:\s-\w+)*\s-i(?!\S|\s"")')
+if [ "$incompatible_sed" ]; then
+	printf "\nWarning: avoid non-portable sed flag -i without backup extension, use -i.bak\n"
+	printf "%s\n\n" "$incompatible_sed"
+fi
 yarn run lint
 "$(yarn bin)/eslint" --rulesdir custom-eslint-rules --ext .ts .

scripts/changelog_mangler.sh

@@ -1,4 +1,4 @@
 #!/bin/sh
 
 # Replace issue numbers in brackets eg (#1337) with a link to the issue on the repository
-sed -i 's; (#\([0-9]*\)); ([#\1](https://github.com/tridactyl/tridactyl/issues/\1));g' CHANGELOG.md
+sed -i.bak 's; (#\([0-9]*\)); ([#\1](https://github.com/tridactyl/tridactyl/issues/\1));g' CHANGELOG.md

scripts/make_tutorial.sh

@@ -16,5 +16,5 @@ do
     sed "/REPLACETHIS/,$ d" tutor.template.html > "$dest$fileroot.html"
     "$(yarn bin)/marked" "$page" >> "$dest$fileroot.html"
     sed "1,/REPLACETHIS/ d" tutor.template.html >> "$dest$fileroot.html"
-    sed -i "s|\.md|.html|g" "$dest$fileroot.html"
+    sed -i.bak "s|\.md|.html|g" "$dest$fileroot.html"
 done