[Refactor] use a different approach to remove trailing slashes

nvm.sh

@@ -258,10 +258,14 @@ if [ -z "${NVM_DIR-}" ]; then
   NVM_DIR="$(nvm_cd ${NVM_CD_FLAGS} "$(dirname "${NVM_SCRIPT_SOURCE:-$0}")" > /dev/null && \pwd)"
   export NVM_DIR
 else
-  while echo "${NVM_DIR}" | nvm_grep -q "/$"; do
-    export NVM_DIR="${NVM_DIR%/}"
-  done
-  nvm_err "Warning: \$NVM_DIR should not have trailing slash"
+  # https://unix.stackexchange.com/a/198289
+  case $NVM_DIR in
+    *[!/]*/)
+      NVM_DIR="${NVM_DIR%"${NVM_DIR##*[!/]}"}"
+      export NVM_DIR
+      nvm_err "Warning: \$NVM_DIR should not have trailing slashes"
+    ;;
+  esac
 fi
 unset NVM_SCRIPT_SOURCE 2> /dev/null