Fix extraneous trailing space for border property (#138)

If just color, or color and style for a border were ommited, an
extraneous space char would be present at the end of the property value
output. This commit fixes this by inserting spaces before values rather
than after.

src/lib.rs

@@ -759,6 +759,29 @@ mod tests {
     "#},
     );
 
+    test(
+      r#"
+      .foo {
+        border: 1px solid currentColor;
+      }
+    "#,
+      indoc! {r#"
+      .foo {
+        border: 1px solid;
+      }
+    "#
+      },
+    );
+
+    minify_test(
+      r#"
+      .foo {
+        border: 1px solid currentColor;
+      }
+    "#,
+      ".foo{border:1px solid}",
+    );
+
     prefix_test(
       r#"
       .foo {

src/properties/border.rs

@@ -162,13 +162,13 @@ impl<S: ToCss + Default + PartialEq> ToCss for GenericBorder<S> {
 
     if self.width != BorderSideWidth::default() {
       self.width.to_css(dest)?;
-      dest.write_str(" ")?;
     }
     if self.style != S::default() {
-      self.style.to_css(dest)?;
       dest.write_str(" ")?;
+      self.style.to_css(dest)?;
     }
     if self.color != CssColor::current_color() {
+      dest.write_str(" ")?;
       self.color.to_css(dest)?;
     }
     Ok(())