API docs: typo fixes in button nested classes docs (#542)

docs/Xamarin.Forms.Core/Xamarin.Forms/Button+ButtonContentLayout+ImagePosition.xml

@@ -52,7 +52,7 @@
         <ReturnType>Xamarin.Forms.Button+ButtonContentLayout+ImagePosition</ReturnType>
       </ReturnValue>
       <Docs>
-        <summary>Indicates that the image will appear at the reght edge of the button.</summary>
+        <summary>Indicates that the image will appear at the right edge of the button.</summary>
       </Docs>
     </Member>
     <Member MemberName="Top">

docs/Xamarin.Forms.Core/Xamarin.Forms/Button+ButtonContentTypeConverter.xml

@@ -42,7 +42,7 @@
       </Parameters>
       <Docs>
         <param name="value">To be added.</param>
-        <summary>Conerts <paramref name="value" /> into a <see cref="T:Xamarin.Forms.Button+ButtonContentLayout" /> object.</summary>
+        <summary>Converts <paramref name="value" /> into a <see cref="T:Xamarin.Forms.Button+ButtonContentLayout" /> object.</summary>
         <returns>To be added.</returns>
         <remarks>To be added.</remarks>
       </Docs>