Fix spelling issue in Migration and Changelog doc

Signed-off-by: yexiaochuan <[email protected]>

Author: XueSongTap

Changelog.md

@@ -830,7 +830,7 @@
 1. Increased Marker coverage
     * [Pull request #738](https://github.com/gazebosim/ign-rendering/pull/738)
 
-1. Added shaderType converage
+1. Added shaderType coverage
     * [Pull request #740](https://github.com/gazebosim/ign-rendering/pull/740)
 
 1. Improved grid coverage
@@ -859,7 +859,7 @@
 1. Update Marker test
     * [Pull request #673](https://github.com/gazebosim/gz-rendering/pull/673)
 
-1. Increase TransformControl test converage
+1. Increase TransformControl test coverage
     * [Pull request #668](https://github.com/gazebosim/gz-rendering/pull/668)
 
 1. Enable ogre2 heightmap test

Migration.md

@@ -92,7 +92,7 @@ formats used in gz-common and gz-msgs.
 
 1. `Scene::SetTime` is often unset. Gazebo's `Ogre2` now defaults to 60hz otherwise rendering won't advance forward.
 	+ Mostly affects Particles.
-	+ Also may affect gaussian postprocessing and other filters dependant on time.
+	+ Also may affect gaussian postprocessing and other filters dependent on time.
 	+ Previous behavior was using real time instead of simulation time, which is wrong.
 	+ See https://github.com/gazebosim/gz-rendering/issues/556 for details.