Update ubuntu 18.04 instructions to install snappy (#248)

If someone configures accumulo to use snappy, its nice if ubuntu already has it installed
diff --git a/docs/ubuntu1804.md b/docs/ubuntu1804.md
index 425cd4a..fba2f53 100644
--- a/docs/ubuntu1804.md
+++ b/docs/ubuntu1804.md
@@ -6,7 +6,7 @@
 
 ```bash
 #install stuff
-sudo apt install openjdk-11-jdk maven git openssh-server wget libxml2-utils make g++
+sudo apt install openjdk-11-jdk maven git openssh-server wget libxml2-utils make g++ libsnappy1v5
 
 #setup passwordless ssh
 ssh-keygen -t rsa -N '' -f ~/.ssh/id_rsa