Classify SVG files as data

This keeps SVG files (which are really just images, even though they
happen to be represented as text) out of repository language statistics.

lib/linguist/languages.yml

@@ -2684,6 +2684,13 @@ STON:
   tm_scope: source.smalltalk
   ace_mode: text
 
+SVG:
+  type: data
+  extensions:
+  - .svg
+  tm_scope: source.xml
+  ace_mode: xml
+
 Sage:
   type: programming
   group: Python
@@ -3199,7 +3206,6 @@ XML:
   - .srdf
   - .stTheme
   - .sublime-snippet
-  - .svg
   - .targets
   - .tmCommand
   - .tmLanguage