Merge branch 'slides/183-type-invariant-graphic-clean-up-and-port-to-svg' into 'master'

Adding type invariant diagram as svg (and removing old png)

Closes #183

See merge request feng/training/material!261

Author: dm-at-ada

courses/fundamentals_of_ada/270_introduction_to_contracts/03-type_invariants.rst

@@ -62,7 +62,7 @@ Type Invariant
 Invariant Over Object Lifetime (Calls)
 ----------------------------------------
 
-.. image:: type_invariant_check_flow.png
+.. image:: type_invariant_check_flow.svg
 
 .. container:: speakernote
 

courses/fundamentals_of_ada/276_type_contracts/02-type_invariants.rst

@@ -48,7 +48,7 @@ Type Invariant Verifications
 Invariant Over Object Lifetime (Calls)
 ----------------------------------------
 
-.. image:: type_invariant_check_flow.png
+.. image:: type_invariant_check_flow.svg
 
 .. container:: speakernote