Check for dch and git requirements
Check for dch and git requirements

Now that we are using dch to edit the Debian package configuration file,
the implication is that `update_version.sh` must be run from a
Debian/Ubuntu environment such as the build VM.

This line checks for dch and, if it is not found, exits with an error
message describing how to install the required dependencies.

jaseg/securedrop,jrosco/securedrop,harlo/securedrop,pwplus/securedrop,ehartsuyker/securedrop,conorsch/securedrop,jaseg/securedrop,heartsucker/securedrop,GabeIsman/securedrop,conorsch/securedrop,conorsch/securedrop,harlo/securedrop,jeann2013/securedrop,ageis/securedrop,chadmiller/securedrop,kelcecil/securedrop,GabeIsman/securedrop,jeann2013/securedrop,jrosco/securedrop,conorsch/securedrop,ehartsuyker/securedrop,GabeIsman/securedrop,harlo/securedrop,GabeIsman/securedrop,heartsucker/securedrop,micahflee/securedrop,jeann2013/securedrop,pwplus/securedrop,ehartsuyker/securedrop,pwplus/securedrop,heartsucker/securedrop,conorsch/securedrop,kelcecil/securedrop,jaseg/securedrop,ageis/securedrop,harlo/securedrop,jaseg/securedrop,harlo/securedrop,heartsucker/securedrop,garrettr/securedrop,chadmiller/securedrop,kelcecil/securedrop,ehartsuyker/securedrop,jaseg/securedrop,kelcecil/securedrop,ehartsuyker/securedrop,jrosco/securedrop,pwplus/securedrop,ageis/securedrop,pwplus/securedrop,jrosco/securedrop,pwplus/securedrop,micahflee/securedrop,jrosco/securedrop,ageis/securedrop,garrettr/securedrop,jeann2013/securedrop,jaseg/securedrop,kelcecil/securedrop,GabeIsman/securedrop,garrettr/securedrop,chadmiller/securedrop,harlo/securedrop,GabeIsman/securedrop,ehartsuyker/securedrop,chadmiller/securedrop,chadmiller/securedrop,jrosco/securedrop,micahflee/securedrop,chadmiller/securedrop,jeann2013/securedrop,jeann2013/securedrop,garrettr/securedrop,heartsucker/securedrop,micahflee/securedrop,kelcecil/securedrop