Fix broken version string and regex check

Author: slarse

setup.py

@@ -7,8 +7,8 @@
 # parse the version instead of importing it to avoid dependency-related crashes
 with open('repomate_plug/__version.py', mode='r', encoding='utf-8') as f:
     line = f.readline()
-    __version__ = line.split('=')[1].strip(" '\"")
-    assert re.match(r'\d\.\d\.\d', __version__)
+    __version__ = line.split('=')[1].strip(" '\"\n")
+    assert re.match(r'^\d\.\d\.\d$', __version__)
 
 test_requirements = ['pytest', 'pytest-cov', 'codecov']
 required = ['pluggy']