changing .gitignore to only ignore bin and build directories created by ...

For those who decide to commit their npm dependencies the current .gitignore for the bin directory breaks the karma module as there are multiple bin directories required. A simple fix is to only ignore the main bin directory "/bin" instead of "bin/" Then if a developer wants to include node_modules and vendor directories they only have to comment out those specific dirs from the .gitignore. A very simple fix for an otherwise time consuming issue to debug.