[librsvg] DrawingCtx: rename vb_stack field to view_box_stack

[Federico Mena Quintero <federico src gnome org>]

commit 19d12a4a319c3bb01137059f241202eccc13e172
Author: Federico Mena Quintero <federico gnome org>
Date:   Tue Sep 4 15:25:49 2018 -0500

    DrawingCtx: rename vb_stack field to view_box_stack

 rsvg_internals/src/drawing_ctx.rs | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/rsvg_internals/src/drawing_ctx.rs b/rsvg_internals/src/drawing_ctx.rs
index ff928318..e45c4f28 100644
--- a/rsvg_internals/src/drawing_ctx.rs
+++ b/rsvg_internals/src/drawing_ctx.rs
@@ -104,7 +104,7 @@ pub struct DrawingCtx<'a> {
     surfaces_stack: Vec<cairo::ImageSurface>,
 
     vb: ViewBox,
-    vb_stack: Vec<ViewBox>,
+    view_box_stack: Vec<ViewBox>,
 
     bbox: BoundingBox,
     bbox_stack: Vec<BoundingBox>,
@@ -159,7 +159,7 @@ impl<'a> DrawingCtx<'a> {
             initial_cr: cr.clone(),
             surfaces_stack: Vec::new(),
             vb: ViewBox::new(0.0, 0.0, vb_width, vb_height),
-            vb_stack: Vec::new(),
+            view_box_stack: Vec::new(),
             bbox: BoundingBox::new(&affine),
             bbox_stack: Vec::new(),
             drawsub_stack: Vec::new(),
@@ -223,14 +223,14 @@ impl<'a> DrawingCtx<'a> {
     }
 
     pub fn push_view_box(&mut self, width: f64, height: f64) -> ViewParams {
-        self.vb_stack.push(self.vb);
+        self.view_box_stack.push(self.vb);
         self.vb = ViewBox::new(0.0, 0.0, width, height);
 
         self.get_view_params()
     }
 
     pub fn pop_view_box(&mut self) {
-        self.vb = self.vb_stack.pop().unwrap();
+        self.vb = self.view_box_stack.pop().unwrap();
     }
 
     pub fn insert_bbox(&mut self, bbox: &BoundingBox) {