Bump margin for PromptTextBox field

Make it look a little more centered if it's a single line text field

Author: donokuda

src/GitHub.VisualStudio/UI/Views/PullRequestCreationView.xaml

@@ -154,7 +154,7 @@
                                     </Border>
                                 </Border>
 
-                                <Grid Margin="1,0,0,0">
+                                <Grid Margin="1,2,0,0">
                                     <ScrollViewer x:Name="PART_ContentHost" Padding="{TemplateBinding Padding}" Focusable="false" HorizontalScrollBarVisibility="Hidden" VerticalScrollBarVisibility="Hidden" VerticalAlignment="Top" Margin="0"/>
                                     <Label x:Name="PromptLabel" HorizontalAlignment="Left"
                                          Foreground="{DynamicResource GitHubVsGrayText}"
@@ -182,9 +182,7 @@
                                     <Setter Property="Foreground" Value="Transparent" />
                                 </DataTrigger>
                             </ControlTemplate.Triggers>
-
                         </ControlTemplate>
-
                     </Setter.Value>
                 </Setter>
             </Style>