Add an instance_double snippet

Tab trigger: `ins`

   ins<tab>
   instance_double(Object)

_cf._ https://relishapp.com/rspec/rspec-mocks/v/3-6/docs/verifying-doubles/using-an-instance-double

Author: jish

Snippets/instance_double.tmSnippet

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>content</key>
+	<string>instance_double(${1:Object})$0</string>
+	<key>name</key>
+	<string>instance_double</string>
+	<key>scope</key>
+	<string>source.ruby.rspec</string>
+	<key>tabTrigger</key>
+	<string>ins</string>
+	<key>uuid</key>
+	<string>C9B5EFEB-757F-432B-8C25-72BCBECAB0B1</string>
+</dict>
+</plist>