Allow usage of search dirs in YangSchema

I want to use YangSchema::addSchemaDirectory in yang-cli, but it doesn't
work if search dirs are disabled.  The real problem is the default usage
of the current working directory as a search dir, so it should be fine
to enable search dirs I supply to it.

Change-Id: I4d4f2d4968987595aa7437fd4ea34195091b99ba
diff --git a/src/yang_schema.cpp b/src/yang_schema.cpp
index fd1b8fe..bbfce7c 100644
--- a/src/yang_schema.cpp
+++ b/src/yang_schema.cpp
@@ -33,7 +33,7 @@
 };
 
 YangSchema::YangSchema()
-    : m_context(std::make_shared<libyang::Context>(nullptr, LY_CTX_DISABLE_SEARCHDIRS | LY_CTX_DISABLE_SEARCHDIR_CWD))
+    : m_context(std::make_shared<libyang::Context>(nullptr, LY_CTX_DISABLE_SEARCHDIR_CWD))
 {
 }