Correct a few grammar errors in docs

doc/namespaces.dox

@@ -434,7 +434,7 @@ See @ref building, @ref cmake and @ref shaders for more information.
 /** @namespace Magnum::Text
 @brief Text rendering
 
-Font texture creation and text layouting.
+Font texture creation and text layout.
 
 This library is built if `WITH_TEXT` is enabled when building Magnum. To use
 this library with CMake, you need to request the `Text` component of the

doc/plugins.dox

@@ -64,7 +64,7 @@ of given type. Magnum provides these plugin interfaces:
 -   @ref Trade::AbstractImageConverter --- conversion among various image
     formats. See `*ImageConverter` classes in the @ref Trade namespace for
     available image converter plugins.
--   @ref Text::AbstractFont --- font loading and glyph layouting. See `*Font`
+-   @ref Text::AbstractFont --- font loading and glyph layout. See `*Font`
     classes in the @ref Text namespace for available font plugins.
 -   @ref Text::AbstractFontConverter --- font and glyph cache conversion. See
     `*FontConverter` classes in the @ref Text namespace for available font