Update and fix dependencies.

The way the dependencies are specified is too specific, and is causing a bunch
of conflicts elsewhere.

Let's update setup.py to do things the right way, then update
requirements-dev.txt with `pip freeze > requirements-dev.txt`.

.travis.yml

@@ -5,7 +5,7 @@ cache: pip
 python: 3.5
 
 install:
-  - pip install -r requirements-dev.txt
+  - pip install .[test]
 
 script:
   - python -m pytest tests/

requirements-dev.txt

@@ -1,7 +1,17 @@
-sortedcontainers>=1.5.9
-requests==2.13.0
-six==1.10.0
-websocket-client==0.40.0
-pymongo==3.5.1
-pytest>=3.3.0
-python-dateutil>=2.7.3
+atomicwrites==1.2.1
+attrs==18.2.0
+cbpro==1.1.4
+certifi==2018.10.15
+chardet==3.0.4
+idna==2.7
+more-itertools==4.3.0
+pluggy==0.8.0
+py==1.7.0
+pymongo==3.7.2
+pytest==4.0.1
+python-dateutil==2.7.5
+requests==2.20.1
+six==1.11.0
+sortedcontainers==2.1.0
+urllib3==1.24.1
+websocket-client==0.54.0

setup.py

@@ -4,14 +4,15 @@
 
 install_requires = [
     'sortedcontainers>=1.5.9',
-    'requests==2.13.0',
-    'six==1.10.0',
-    'websocket-client==0.40.0',
-    'pymongo==3.5.1'
+    'requests>=2.13.0',
+    'six>=1.10.0',
+    'websocket-client>=0.40.0',
+    'pymongo>=3.5.1',
 ]
 
 tests_require = [
     'pytest',
+    'python-dateutil>=2.7.5',
     ]
 
 with open("README.md", "r") as fh:
@@ -27,6 +28,9 @@
     packages=find_packages(),
     install_requires=install_requires,
     tests_require=tests_require,
+    extras_require={
+        'test': tests_require,
+    },
     description='The unofficial Python client for the Coinbase Pro API',
     long_description=long_description,
     long_description_content_type="text/markdown",