fix SVG mime type (allure-framework#841)

Author: harmin-parra

allure-python-commons/src/types.py

@@ -53,7 +53,7 @@ def __init__(self, mime_type, extension):
 
  PNG = ("image/png", "png")
  JPG = ("image/jpg", "jpg")
- SVG = ("image/svg-xml", "svg")
+ SVG = ("image/svg+xml", "svg")
  GIF = ("image/gif", "gif")
  BMP = ("image/bmp", "bmp")
  TIFF = ("image/tiff", "tiff")