Use upstream Doxygen archive

Author: bstaletic

.travis.yml

@@ -18,8 +18,8 @@ matrix:
     - $PY_CMD -m pip install --user --upgrade pip wheel
     install:
     - $PY_CMD -m pip install --user --upgrade sphinx sphinx_rtd_theme breathe flake8 pep8-naming pytest
-    - curl -fsSL ftp://ftp.stack.nl/pub/users/dimitri/doxygen-1.8.12.linux.bin.tar.gz | tar xz
-    - export PATH="$PWD/doxygen-1.8.12/bin:$PATH"
+    - curl -fsSL https://sourceforge.net/projects/doxygen/files/rel-1.8.15/doxygen-1.8.15.linux.bin.tar.gz/download | tar xz
+    - export PATH="$PWD/doxygen-1.8.15/bin:$PATH"
     script:
     - tools/check-style.sh
     - flake8