Allow `-` (dash) in process type

[benspaulding]

This change adds - (dash) to the list of valid characters for a process type. I propose this change because it seems to be the de facto Procfile standard.

I recently made a VS Code extension with syntax highlighting for Procfiles. In my testing I found that Honcho is the only Foreman clone that does not allow dashes in the process type. Allowing it would bring it in line with Foreman and the others.

Here is an excerpt from the project README that details my findings:

---

Foreman & Clones

The most used and robust are:

• Foreman (Ruby)
• Honcho (Python)
• Goreman (Go)

Others include:

• node-foreman (Node) — n.b. How on earth is this not named “Noreman”? I insist on referring to it as such!
• Shoreman (Shell)
• forego (Go)

[…]

Procfile	Foreman	Honcho	Goreman	Noreman	Shoreman	forego
n0 …	#	#	#	✗	✗	✗
n1: …	✓	✓	✓	✓	✓	✓
n2: …	#	#	✓	✗	✓	✗
n3 : …	#	#	✓	✗	✓	✗
n4:…	✓	✓	✓	✓	✗	✓
n 5: …	#	#	✓	✗	✓ / ✗	✗
# n6: …	#	#	#	#	#	✗
#n7: …	#	#	#	#	#	✗
n-8: …	✓	#	✓	✓	✓	✓
n9 :…	#	#	✓	✗	✓	✗

legend
valid process	✓
comment / ignored	#
error / hang	✗

---

Closes #206.

[nickstenning]

Thanks! This LGTM. The build is failing because I need to remove support for Python 2.6, but I'm going to go ahead and merge this as everything other than 2.6 is passing.

[nickstenning]

Actually just spotted one change (to the text of the docs) and if you could make that change and rebase on master that would be fab. Rebasing should fix the Python 2.6 build failure thanks to #216.

[nickstenning]

Great, thanks! LGTM.