fix dot syntax generated by graphviz target
fix test for dot generator
Fix travis builds
Merge pull request #546 from ulfhermann/master

fix graphviz syntax
fixed key serialization
added test
Merge pull request #557 from MaksSlesarenko/fix-for-date-primary-key

fixed key serialization
fix serialization for all temporal type
Merge pull request #558 from MaksSlesarenko/fix-for-temporal-types

fix serialization for all temporal type
Avoid escaping single quote in a string

See: https://github.com/propelorm/Propel/pull/558/files#r2616005