GUACAMOLE-928: Merge keep FreeRDP plugins of Docker image within /usr/local/guacamole

diff --git a/src/guacd-docker/bin/build-guacd.sh b/src/guacd-docker/bin/build-guacd.sh
index 4714743..9e263ae 100755
--- a/src/guacd-docker/bin/build-guacd.sh
+++ b/src/guacd-docker/bin/build-guacd.sh
@@ -43,7 +43,7 @@
 
 cd "$BUILD_DIR"
 autoreconf -fi
-./configure --prefix="$PREFIX_DIR" --disable-guaclog
+./configure --prefix="$PREFIX_DIR" --disable-guaclog --with-freerdp-plugin-dir="$PREFIX_DIR/lib/freerdp2"
 make
 make install
 ldconfig