add timeout

.tools/convert-markdown-into-ipynb-and-test.sh

 #!/bin/bash
 command -v go >/dev/null 2>&1
-if [ $? -ne 0 ]; then
+if [[ $? -ne 0 ]]; then
     echo >&2 "Please install go https://golang.org/doc/install#install"
     exit 1
 fi
@@ -13,7 +13,7 @@ cd $cur_path/../
 #convert md to ipynb
 for file in */{README,README\.en}.md ; do
     ~/go/bin/markdown-to-ipynb < $file > ${file%.*}".ipynb"
-    if [ $? -ne 0 ]; then
+    if [[ $? -ne 0 ]]; then
         echo >&2 "markdown-to-ipynb $file error"
         exit 1
     fi
@@ -29,7 +29,19 @@ for file in */{README,README\.en}.ipynb ; do
     cd $(dirname $file) > /dev/null
 
     echo "begin test $file"
-    jupyter nbconvert --to python $(basename $file) --stdout | python
+    if [[ $(dirname $file) == "08.recommender_system" ]]; then
+       timeout -s SIGKILL 30 bash -c \
+           "jupyter nbconvert --to python $(basename $file) --stdout  | \
+           sed  's/get_ipython()\.magic(.*'\''matplotlib inline'\'')/\#matplotlib inline/g' | \
+           sed '/^# coding: utf-8/a\import matplotlib\nmatplotlib.use('\''Agg'\'')' | python"
+    else
+       timeout -s SIGKILL 30  bash -c "jupyter nbconvert --to python $(basename $file) --stdout | python" 
+    fi
+
+    if [[ $? -ne 0 && $? -ne 124 && $? -ne 137 ]]; then
+        echo >&2 "exec $file error!"
+        exit 1
+    fi
 
     popd > /dev/null
     #break