Update README.md

sweet clang analysis badge thanks to @Hinidu!
travis.sh: Update sources before installing packages.
Merge pull request #1038 '[RDY] Update APT package sources in travis.sh.'
bugfix: set empty string as default for ipy/icpb to avoid segfault

Fixes #1039
Merge PR #1040 'Fix segfault caused by default value of ipy/icpb options'