check error of make html (opea-project#236)

Signed-off-by: alexsin368 <alex.sin@intel.com>

Author: NeoZhangJianyu

scripts/build.sh

@@ -41,6 +41,14 @@ cd docs
 make clean
 make html
 
+retval=$?
+if [ $retval -ne 0 ]; then
+  echo "make html is error"
+  exit 1
+else
+  echo "Done"
+fi
+
 if [ ! -d _build/html ]; then
   echo "Build online doc is wrong!"
   exit 1