Update sed command (per https://stackoverflow.com/a/19457213)

Author: jsh9

update_version.sh

@@ -1,7 +1,7 @@
 echo "Updating version number in files: from $1 to $2"
-sed -i "s/$1/$2/g" README.md
-sed -i "s/$1/$2/g" setup.py
-sed -i "s/$1/$2/g" ./doc/source/index.rst
-sed -i "s/$1/$2/g" ./doc/source/conf.py
-sed -i "s/$1/$2/g" ./doc/source/installation_guide.rst
-sed -i "s/$1/$2/g" ./plot_utils/__init__.py
+sed -i "" -e "s/$1/$2/g" README.md
+sed -i "" -e "s/$1/$2/g" setup.py
+sed -i "" -e "s/$1/$2/g" ./doc/source/index.rst
+sed -i "" -e "s/$1/$2/g" ./doc/source/conf.py
+sed -i "" -e "s/$1/$2/g" ./doc/source/installation_guide.rst
+sed -i "" -e "s/$1/$2/g" ./plot_utils/__init__.py