Fix typo in readme.md (#702)

Rename 'zipper' -> 'zypper'

Author: dreyman

README.md

@@ -25,7 +25,7 @@ You'll also need the ```glib-compile-schemas``` and  ```gdk-pixbuf-pixdata``` co
 |Distro|Commands|
 |:----:|:----:|
 |![arch][arch]  ![antergos][antergos]|`sudo pacman -S glib2 gdk-pixbuf2`|
-|![opensuse][opensuse]|`sudo zipper install glib2-devel gdk-pixbuf-devel`|
+|![opensuse][opensuse]|`sudo zypper install glib2-devel gdk-pixbuf-devel`|
 |![fedora][fedora]|`sudo dnf install glib2-devel gdk-pixbuf2-devel`|
 |![debian][debian]  ![ubuntu][ubuntu]|`sudo apt-get install ruby-sass libglib2.0-dev libgdk-pixbuf2.0-dev libxml2-utils`|