Fix last character cut in html-report if file does not end with newline (#3466)

Author: ilinum

mypy/report.py

@@ -334,7 +334,7 @@ def on_file(self,
                 etree.SubElement(root, 'line',
                                  number=str(lineno),
                                  precision=stats.precision_names[status],
-                                 content=line_text[:-1])
+                                 content=line_text.rstrip('\n'))
         # Assumes a layout similar to what XmlReporter uses.
         xslt_path = os.path.relpath('mypy-html.xslt', path)
         transform_pi = etree.ProcessingInstruction('xml-stylesheet',