try qt4 before qt5, since qt5 still seems flakey in many python distros (closes #278)

Author: stevengj

src/PyPlot.jl

@@ -106,7 +106,7 @@ function find_backend(matplotlib::PyObject)
     elseif is_apple() && conda # partially work around #164
         guis = [:qt5, :qt4, :tk, :wx, :gtk, :gtk3]
     else
-        guis = [:tk, :qt5, :qt4, :wx, :gtk, :gtk3]
+        guis = [:tk, :qt4, :qt5, :wx, :gtk, :gtk3]
     end
     options = [(g,gui2matplotlib[g]) for g in guis]