Remove dependency on libgconf2-4 in favor of libgconf-2-4 for compatibility

[credmp]

The below contents is from #141. Ubuntu has removed the meta package libgconf2-4 in favor of the actual package libgconf-2-4 (notice the dash). As a result none of the packages built with electron-installer-debian will install on recent Ubuntu installations. #141 was closed without a solution as a result.

What version of electron-installer-debian are you using?
0.8.1
What version of node and npm are you using?
v6.11.3 and 3.10.10
What operating system are you using?

* To compile, Linux Mint 18.1 Mate 64bits

* To install the .deb, Huayra Linux 64 bits, based on Debian 8.3 and Mate 1.8.1

Can you compile the example app successfully?
yes

What did you do? Please include the configuration you are using for electron-installer-debian.
In Linux Mint:

 * `electron-installer-debian --src (my source) --dest (my dest) --arch amd64`

In Huayra:

 * I double click the .deb. I answer "Yes" to "Do you want to install this package". After starting the unpackaging process, it says  (In spanish) "Failure when installing".

 * I then tried a `sudo dpkg -i` and says that it has unmet dependencies with "libgconf2-4", yet however **I do have installed the package libgconf-2-4** (note the extra hyphen). [Here](https://packages.debian.org/sid/libgconf2-4) it says that libgconf2-4 is a _dummy package_, so I think that every repository that has libgconf2-4 also has libgconf-2-4, but it's not the case in the other way (In Huayra repositories they only have the libgconf-2-4 package, which is exactly the same).

What did you expect to happen?
I expected to be able to install the .deb package in debian.

What actually happened?
It didn't.

[malept]

Your version of electron-installer-debian is very out of date. Please use the newest version.

[credmp]

Indeed, the project I was using is indeed reliant on an old version. This issue was fixed with #185.