[Refactor] Speedup nvm_list_aliases()
diff --git a/nvm.sh b/nvm.sh
index 23b539a..9299467 100644
--- a/nvm.sh
+++ b/nvm.sh
@@ -747,25 +747,42 @@
   NVM_ALIAS_DIR="$(nvm_alias_path)"
   command mkdir -p "${NVM_ALIAS_DIR}/lts"
 
-  local ALIAS_PATH
-  for ALIAS_PATH in "${NVM_ALIAS_DIR}/${ALIAS}"*; do
-    NVM_NO_COLORS="${NVM_NO_COLORS-}" NVM_CURRENT="${NVM_CURRENT}" nvm_print_alias_path "${NVM_ALIAS_DIR}" "${ALIAS_PATH}"
-  done
+  (
+    local ALIAS_PATH
+    for ALIAS_PATH in "${NVM_ALIAS_DIR}/${ALIAS}"*; do
+      NVM_NO_COLORS="${NVM_NO_COLORS-}" NVM_CURRENT="${NVM_CURRENT}" nvm_print_alias_path "${NVM_ALIAS_DIR}" "${ALIAS_PATH}" &
+    done
+    wait
+  ) | sort
 
-  local ALIAS_NAME
-  for ALIAS_NAME in "$(nvm_node_prefix)" "stable" "unstable" "$(nvm_iojs_prefix)"; do
+  (
+    local ALIAS_NAME
+    for ALIAS_NAME in "$(nvm_node_prefix)" "stable" "unstable"; do
+      {
+        if [ ! -f "${NVM_ALIAS_DIR}/${ALIAS_NAME}" ] && ([ -z "${ALIAS}" ] || [ "${ALIAS_NAME}" = "${ALIAS}" ]); then
+          NVM_NO_COLORS="${NVM_NO_COLORS-}" NVM_CURRENT="${NVM_CURRENT}" nvm_print_default_alias "${ALIAS_NAME}"
+        fi
+      } &
+    done
+    wait
+    ALIAS_NAME="$(nvm_iojs_prefix)"
     if [ ! -f "${NVM_ALIAS_DIR}/${ALIAS_NAME}" ] && ([ -z "${ALIAS}" ] || [ "${ALIAS_NAME}" = "${ALIAS}" ]); then
       NVM_NO_COLORS="${NVM_NO_COLORS-}" NVM_CURRENT="${NVM_CURRENT}" nvm_print_default_alias "${ALIAS_NAME}"
     fi
-  done
+  ) | sort
 
-  local LTS_ALIAS
-  for ALIAS_PATH in "${NVM_ALIAS_DIR}/lts/${ALIAS}"*; do
-    LTS_ALIAS="$(NVM_NO_COLORS="${NVM_NO_COLORS-}" NVM_LTS=true nvm_print_alias_path "${NVM_ALIAS_DIR}" "${ALIAS_PATH}")"
-    if [ -n "${LTS_ALIAS}" ]; then
-      nvm_echo "${LTS_ALIAS}"
-    fi
-  done
+  (
+    local LTS_ALIAS
+    for ALIAS_PATH in "${NVM_ALIAS_DIR}/lts/${ALIAS}"*; do
+      {
+        LTS_ALIAS="$(NVM_NO_COLORS="${NVM_NO_COLORS-}" NVM_LTS=true nvm_print_alias_path "${NVM_ALIAS_DIR}" "${ALIAS_PATH}")"
+        if [ -n "${LTS_ALIAS}" ]; then
+          nvm_echo "${LTS_ALIAS}"
+        fi
+      } &
+    done
+    wait
+  ) | sort
   return
 }