gnu: asymptote: Add missing input.

* gnu/packages/plotutils.scm (asymptote)[inputs]: Add missing input for GUI.

gnu/packages/plotutils.scm

@@ -217,6 +217,7 @@ (define-public asymptote
        ("libgc" ,libgc)
        ("python" ,python)
        ("python-cson" ,python-cson)
+       ("python-numpy" ,python-numpy)
        ("python-pyqt" ,python-pyqt)
        ("readline" ,readline)
        ("zlib" ,zlib)))