Log Message:
gtksourceview4: update to 4.0.3.

News in 4.0.3, 2018-09-05
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* New syntax highlighting definition file for: Gradle and Logtalk.
* Improvements to the syntax highlighting of: JavaScript, LaTeX, Haskell, C++,
  GLSL, and Markdown.
* Performance improvements to space drawing.
* Various memory leak fixes.
* Translation updates.