Specify the oemof dependency correctly

The egg fragment has to have the correct version suffix and the
dependency has to be pinned, probably because the `'.dev0'` suffix
prohibits comparison to purely numerical versions. This setup finally
makes the tests pass again.

docs/requirements.txt

@@ -2,5 +2,5 @@ sphinx>=1.3
 sphinx-rtd-theme
 -e .
 
-git+https://git@github.com/oemof/oemof.git@features/move-datapackage-reader-into-standalone-package#egg=oemof
+git+https://git@github.com/oemof/oemof.git@features/move-datapackage-reader-into-standalone-package#egg=oemof-0.2.4.dev0
 

setup.py

@@ -65,7 +65,7 @@ def read(*names, **kwargs):
     ],
     install_requires=[
         'datapackage',
-        'oemof',
+        'oemof==0.2.4.dev0',
     ],
     extras_require={
         # eg:
@@ -75,5 +75,5 @@ def read(*names, **kwargs):
     dependency_links=[
         ('git+https://git@github.com/oemof/oemof.git'
          '@features/move-datapackage-reader-into-standalone-package'
-         '#egg=oemof')],
+         '#egg=oemof-0.2.4.dev0')],
 )