Change ABI version to 0.2.1 (proxy-wasm#45)

This is necessary because the new proxy_get_log_level function
only exists there.

Signed-off-by: Gregory Brail <[email protected]>

Author: gbrail

proxy_wasm_intrinsics.cc

@@ -17,7 +17,7 @@
 #include "proxy_wasm_intrinsics.h"
 
 // Required Proxy-Wasm ABI version.
-extern "C" PROXY_WASM_KEEPALIVE void proxy_abi_version_0_2_0() {}
+extern "C" PROXY_WASM_KEEPALIVE void proxy_abi_version_0_2_1() {}
 
 static std::unordered_map<std::string, RootFactory> *root_factories = nullptr;
 static std::unordered_map<std::string, ContextFactory> *context_factories = nullptr;