diff --git a/doc/using_procfiles.rst b/doc/using_procfiles.rst
index 02cd95b..d11dc91 100644
--- a/doc/using_procfiles.rst
+++ b/doc/using_procfiles.rst
@@ -18,10 +18,10 @@ source tree that contains zero or more lines of the form::
 
     <process type>: <command>
 
-The ``process type`` is a string which may contain alphanumerics and underscores
-(``[A-Za-z0-9_]+``), and uniquely identifies one type of process which can be
-run to form your application. For example: ``web``, ``worker``, or
-``my_process_123``.
+The ``process type`` is a string which may contain alphanumerics as well as
+underscores and dashes (``[A-Za-z0-9_-]+``), and uniquely identifies one type
+of process which can be run to form your application. For example: ``web``,
+``worker``, or ``my_process_123``.
 
 ``command`` is a shell commandline which will be executed to spawn a process of
 the specified type.
diff --git a/honcho/environ.py b/honcho/environ.py
index 646d950..09448f3 100644
--- a/honcho/environ.py
+++ b/honcho/environ.py
@@ -13,7 +13,7 @@ if compat.ON_WINDOWS:
     import ctypes
 
 
-PROCFILE_LINE = re.compile(r'^([A-Za-z0-9_]+):\s*(.+)$')
+PROCFILE_LINE = re.compile(r'^([A-Za-z0-9_-]+):\s*(.+)$')
 
 
 class Env(object):

diff --git a/tests/test_environ.py b/tests/test_environ.py
index c7260a4..a9720d7 100644
--- a/tests/test_environ.py
+++ b/tests/test_environ.py
@@ -155,10 +155,17 @@ def test_environ_parse(content, commands):
     [
         # Invalid characters
         """
-        -foo: command
+        +foo: command
         """,
         {}
     ],
+    [
+        # Valid -/_ characters
+        """
+        -foo_bar: command
+        """,
+        {'-foo_bar': 'command'}
+    ],
     [
         # Shell metacharacters
         """

Dashes in process types
I believe that process types, according to this [Heroku page](https://devcenter.heroku.com/articles/procfile), must be alphanumeric.

If I create a Procfile with the following content

```
process-type-with-dashes: python -c 'print("hello")'
```

and then run `honcho start`, honcho fails silently.

Also, when I run `honcho check`, it says it is a valid Procfile.

Perhaps it would be helpful if:
- `honcho start` would complain if there is an invalid Procfile
- `honcho check` complains if the process types have dashes

I am using honcho v1.0.1 with python 3.7.0 on macOS.

Thank you for all of your work, I wish I had time to create a PR for this, but I figured creating an issue was better than nothing.
tests/test_environ.py::test_parse_procfile[\n
tests/test_environ.py::test_environ_parse[\n tests/test_environ.py::test_parse_procfile_ordered tests/test_environ.py::TestProcfile::test_has_no_processes_after_init tests/test_environ.py::TestProcfile::test_add_process tests/test_environ.py::TestProcfile::test_add_process_ensures_unique_name tests/test_environ.py::test_expand_processes_name tests/test_environ.py::test_expand_processes_name_multiple tests/test_environ.py::test_expand_processes_name_concurrency tests/test_environ.py::test_expand_processes_name_concurrency_multiple tests/test_environ.py::test_expand_processes_command tests/test_environ.py::test_expand_processes_port_not_defaulted tests/test_environ.py::test_expand_processes_port tests/test_environ.py::test_expand_processes_port_multiple tests/test_environ.py::test_expand_processes_port_from_env tests/test_environ.py::test_expand_processes_port_from_env_coerced_to_number tests/test_environ.py::test_expand_processes_port_from_env_overrides tests/test_environ.py::test_expand_processes_port_concurrency tests/test_environ.py::test_expand_processes_quiet tests/test_environ.py::test_expand_processes_quiet_multiple tests/test_environ.py::test_expand_processes_env tests/test_environ.py::test_expand_processes_env_multiple tests/test_environ.py::test_set_env_process_name