Update base64.yar Fix #153

Crypto/base64.yar

@@ -2,8 +2,11 @@ rule contentis_base64 : Base64
 {
     meta:
         author = "Jaume Martin"
+        description = "This rule finds for base64 strings"
+        version = "0.2"
+        notes = "https://github.com/Yara-Rules/rules/issues/153"
     strings:
-        $a = /([A-Za-z0-9+\/]{4})*([A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?/
+        $a = /([A-Za-z0-9+\/]{4}){3,}([A-Za-z0-9+\/]{2}==|[A-Za-z0-9+\/]{3}=)?/
     condition:
         $a
 }