improve pipupdate() reliablity

functions.sh

@@ -226,8 +226,11 @@ function gitupdate(){
 }
 
 function pipupdate(){
-    for pip in pip2 pip2; do
-         $pip freeze --local | grep -v '^\-e' | cut -d = -f 1 | xargs -n1 $pip install -U
+    for pip in pip2 pip3; do
+        if [ -z $pip ]; then
+            continue
+        fi
+        $pip freeze --local | grep -v '^\-e' | cut -d = -f 1 | xargs -n1 $pip install -U
     done
 }