Alerts: Change 'Alias' Field To 'Shorturl'

Suggested by Saïvann (thanks!)

_alerts/2012-02-18-protocol-change.html

@@ -1,6 +1,6 @@
 ---
 title: "February 20, 2012 Protocol Changes"
-alias: "feb20"
+shorturl: "feb20"
 active: false
 banner: ""
 ---

_alerts/2012-03-16-critical-vulnerability.html

@@ -1,6 +1,6 @@
 ---
 title: "Potentially Critical Security Vulnerability"
-alias: "critfix"
+shorturl: "critfix"
 active: false
 banner: ""
 ---

_alerts/2012-05-14-dos.html

@@ -1,6 +1,6 @@
 ---
 title: "CVE-2012-2459: Critical Vulnerability (denial-of-service)"
-alias: "dos"
+shorturl: "dos"
 active: false
 banner: ""
 ---

_alerts/2013-03-11-chain-fork.html

@@ -1,6 +1,6 @@
 ---
 title: "11/12 March 2013 Chain Fork Information"
-alias: "chainfork"
+shorturl: "chainfork"
 active: false
 banner: ""
 ---

_alerts/2013-03-15-upgrade-deadline.html

@@ -1,6 +1,6 @@
 ---
 title: "15 May 2013 Upgrade Deadline"
-alias: "may15"
+shorturl: "may15"
 active: false
 banner: ""
 ---

_alerts/2013-08-11-android.html

@@ -1,7 +1,7 @@
 ---
 title: "Android Security Vulnerability"
 active: false
-alias: "android"
+shorturl: "android"
 banner: ""
 ---
 

_alerts/2014-04-11-heartbleed.html

@@ -1,6 +1,6 @@
 ---
 title: "OpenSSL Heartbleed vulnerability"
-alias: "heartbleed"
+shorturl: "heartbleed"
 active: false
 banner: ""
 ---

_alerts/2015-07-04-spv-mining.md

@@ -1,6 +1,6 @@
 ---
 title: "Some Miners Generating Invalid Blocks"
-alias: "spv-mining"
+shorturl: "spv-mining"
 active: false
 #banner: "WARNING: many wallets currently vulnerable to double-spending of confirmed transactions (click here to read)"
 bannerclass: "alert"