Make monokai the default colorscheme

Monokai is a better default colorscheme because it has a better 16
color approximation than zenburn. On 16 color terminals, it looks like
zenburn is not syntax highlighting anything.

cmd/micro/settings.go

@@ -178,7 +178,7 @@ func DefaultGlobalSettings() map[string]interface{} {
 		"autoindent":   true,
 		"autosave":     false,
 		"colorcolumn":  float64(0),
-		"colorscheme":  "zenburn",
+		"colorscheme":  "default",
 		"cursorline":   true,
 		"ignorecase":   false,
 		"indentchar":   " ",