Output coverage to coverage.xml.

This avoids https://bitbucket.org/ned/coveragepy/issues/400/

.coveragerc

@@ -14,4 +14,4 @@ exclude_lines =
     if __name__ == ["']__main__["']:
 
 [xml]
-output=.coverage.xml
+output=coverage.xml

scripts/dev/check_coverage.py

@@ -143,7 +143,7 @@ def main():
     utils.change_cwd()
 
     try:
-        with open('.coverage.xml', encoding='utf-8') as f:
+        with open('coverage.xml', encoding='utf-8') as f:
             messages = check(f, PERFECT_FILES)
     except Skipped as e:
         print(e)
@@ -152,7 +152,7 @@ def main():
     for msg in messages:
         print(msg)
 
-    os.remove('.coverage.xml')
+    os.remove('coverage.xml')
     return 1 if messages else 0