hooks: fix newline injection on MacOS

Because MacOS `sed` just needs newlines to be escaped differently.

Signed-off-by: Jakub Sokołowski <jakub@status.im>

scripts/hooks/prepare-commit-msg

@@ -1,10 +1,13 @@
 #!/usr/bin/env bash
-set -euo pipefail
+set -eo pipefail
 
 if [[ -z $(git diff --cached --name-only -r | grep status-go-version.json) ]]; then
   exit 0 # No status-go-version.json changes found.
 fi
 
+# MacOS sed is garbage and interprets newlines differently.
+[[ "$(uname)" -eq "Darwin" ]] && NL=$'\\\n' || NL="\n"
+
 MERGE_BASE=$(git merge-base -a develop "$(git rev-parse --abbrev-ref HEAD)" develop)
 GO_COMMIT_MERGE_BASE=$(git show "${MERGE_BASE}":status-go-version.json | awk -F'"' '/commit-sha1/{print $4}')
 GO_COMMIT_CURRENT=$(awk -F'"' '/commit-sha1/{print $4}' status-go-version.json)
@@ -16,7 +19,7 @@ COMMIT_MSG_FILE=$1
 # Check if the commit message already contains the link (rebase) and update otherwise insert into line2
 if ! grep -qF "${GITHUB_LINK_PREFIX}" "${COMMIT_MSG_FILE}" >/dev/null; then
   sed -in'' -e "2i\\
-\n${GITHUB_LINK}" "${COMMIT_MSG_FILE}"
+${NL}${GITHUB_LINK}" "${COMMIT_MSG_FILE}"
 else
   sed -in'' -e "s;^${GITHUB_LINK_PREFIX}.*$;${GITHUB_LINK};" "${COMMIT_MSG_FILE}"
 fi