Fix Shellcheck SC2046: Quote to prevent word split

Quote this to prevent word splitting

https://www.shellcheck.net/wiki/SC2046

Signed-off-by: Dan Callahan <danc@element.io>

scripts-dev/check_line_terminators.sh

@@ -25,7 +25,7 @@
 # terminators are found, 0 otherwise.
 
 # cd to the root of the repository
-cd `dirname $0`/.. || exit
+cd "`dirname $0`/.." || exit
 
 # Find and print files with non-unix line terminators
 if find . -path './.git/*' -prune -o -type f -print0 | xargs -0 grep -I -l $'\r$'; then