add fish config

fish/functions/_nvm_index_update.fish

@@ -0,0 +1,20 @@
+function _nvm_index_update
+    test ! -d $nvm_data && command mkdir -p $nvm_data
+
+    set --local index $nvm_data/.index
+
+    if not command curl -q --location --silent $nvm_mirror/index.tab >$index.temp
+        command rm -f $index.temp
+        echo "nvm: Can't update index, host unavailable: \"$nvm_mirror\"" >&2
+        return 1
+    end
+
+    command awk -v OFS=\t '
+        /v0.9.12/ { exit } # Unsupported
+        NR > 1 {
+            print $1 (NR == 2  ? " latest" : $10 != "-" ? " lts/" tolower($10) : "")
+        }
+    ' $index.temp >$index
+
+    command rm -f $index.temp
+end