change the default dpi from 96 to 100 so that we get readable fonts

gfx/src/gtk/nsDeviceContextGTK.cpp

@@ -77,7 +77,7 @@ NS_IMETHODIMP nsDeviceContextGTK::Init(nsNativeWidget aNativeWidget)
 
   mWidget = aNativeWidget;
 
-  static nscoord dpi = 96;
+  static nscoord dpi = 100;
   static int initialized = 0;
   if (!initialized) {
     initialized = 1;