Ensure line endings for binary files are not modified in Git

This commit is necessary in order to upgrade the Gradle wrapper, since
the recent attempt to do so ended up in a corrupted JAR file for the
Gradle wrapper.

.gitattributes

@@ -3,3 +3,14 @@
 
 # Ensure that line endings for multipart files in spring-web are not modified.
 *.multipart -text
+
+# Ensure that line endings for DOS batch files are not modified.
+*.bat -text
+
+# Ensure the following are treated as binary.
+*.gif   binary
+*.jar   binary
+*.jpeg  binary
+*.jpg   binary
+*.png   binary
+*.vsd   binary