Fix some issues reported by shellcheck

libexec/rbenv-rehash

@@ -83,7 +83,7 @@ remove_outdated_shims() {
 list_executable_names() {
   local version file
   rbenv-versions --bare --skip-aliases | \
-  while read version; do
+  while read -r version; do
     for file in "${RBENV_ROOT}/versions/${version}/bin/"*; do
       echo "${file##*/}"
     done
@@ -136,6 +136,7 @@ shopt -s nullglob
 # executables.
 create_prototype_shim
 remove_outdated_shims
+# shellcheck disable=SC2046
 make_shims $(list_executable_names | sort -u)