Add shelf to JetBrains.gitignore

Global/JetBrains.gitignore

@@ -4,7 +4,8 @@
 # User-specific stuff
 .idea/**/workspace.xml
 .idea/**/tasks.xml
-.idea/dictionaries
+.idea/**/dictionaries
+.idea/**/shelf
 
 # Sensitive or high-churn files
 .idea/**/dataSources/