Update default user-agent (#2785)

* Updated default user agent so that it includes only the requests
version;
* Added PyCharm / IDEA project directory to `.gitignore`.

.gitignore

@@ -15,6 +15,7 @@ requests.egg-info/
 *.swp
 *.egg
 env/
+.idea/
 
 .workon
 

requests/utils.py

@@ -552,33 +552,7 @@ def select_proxy(url, proxies):
 
 def default_user_agent(name="python-requests"):
     """Return a string representing the default user agent."""
-    _implementation = platform.python_implementation()
-
-    if _implementation == 'CPython':
-        _implementation_version = platform.python_version()
-    elif _implementation == 'PyPy':
-        _implementation_version = '%s.%s.%s' % (sys.pypy_version_info.major,
-                                                sys.pypy_version_info.minor,
-                                                sys.pypy_version_info.micro)
-        if sys.pypy_version_info.releaselevel != 'final':
-            _implementation_version = ''.join([_implementation_version, sys.pypy_version_info.releaselevel])
-    elif _implementation == 'Jython':
-        _implementation_version = platform.python_version()  # Complete Guess
-    elif _implementation == 'IronPython':
-        _implementation_version = platform.python_version()  # Complete Guess
-    else:
-        _implementation_version = 'Unknown'
-
-    try:
-        p_system = platform.system()
-        p_release = platform.release()
-    except IOError:
-        p_system = 'Unknown'
-        p_release = 'Unknown'
-
-    return " ".join(['%s/%s' % (name, __version__),
-                     '%s/%s' % (_implementation, _implementation_version),
-                     '%s/%s' % (p_system, p_release)])
+    return '%s/%s' % (name, __version__)
 
 
 def default_headers():