fix send_request version message

bal.py

@@ -47,18 +47,19 @@ class BalConfig:
 
 
 class BalPlugin(BasePlugin):
-    LATEST_VERSION = "1"
-    KNOWN_VERSIONS = ("0", "1")
-    assert LATEST_VERSION in KNOWN_VERSIONS
+    _version=None
 
-    def version():
-        try:
-            f = ""
-            with open("VERSION", "r") as fi:
-                f = str(fi.readline())
-            return f
-        except Exception:
-            return "unknown"
+    def version(self):
+        if not self._version:
+            try:
+                f = ""
+                with open("{}/VERSION".format(self.plugin_dir), "r") as fi:
+                    f = str(fi.read())
+                self._version = f.strip()
+            except Exception as e:
+                _logger.error(f"failed to get version: {e}")
+                self._version="unknown"
+        return self._version        
 
     SIZE = (159, 97)