Add Linux Mint 18 case to switch statement

/etc/os-release file on LM18:

NAME="Linux Mint"
VERSION="18 (Sarah)"
ID=linuxmint
ID_LIKE=ubuntu
PRETTY_NAME="Linux Mint 18"
VERSION_ID="18"
HOME_URL="http://www.linuxmint.com/"
SUPPORT_URL="http://forums.linuxmint.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/linuxmint/"
UBUNTU_CODENAME=xenial

Author: kamszyc

src/platform.ts

@@ -93,9 +93,17 @@ export function getCurrentPlatform() {
                     return Platform.Ubuntu16;
                 }
 
+                break;
+            case 'linuxmint':
+                const lmVersionId = getValue("VERSION_ID");
+                if (lmVersionId.startsWith("18")) {
+                    // Linux Mint 18 is binary compatible with Ubuntu 16.04
+                    return Platform.Ubuntu16;
+                }
+
                 break;
         }
     }
 
     return Platform.Unknown;	
-}
+}