build: fix indentation in node.gyp

One line in node.gyp was indented using a mix of a tab and spaces,
convert it to all spaces.

PR-URL: nodejs/node#15051
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Yuta Hiroto <hello@about-hiroppy.com>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

node.gyp

@@ -649,7 +649,7 @@
       'conditions': [
         ['node_target_type!="static_library"', {
           'libraries': [
-	    '<(OBJ_GEN_PATH)<(OBJ_SEPARATOR)node_javascript.<(OBJ_SUFFIX)',
+            '<(OBJ_GEN_PATH)<(OBJ_SEPARATOR)node_javascript.<(OBJ_SUFFIX)',
             '<(OBJ_PATH)<(OBJ_SEPARATOR)node_debug_options.<(OBJ_SUFFIX)',
             '<(OBJ_PATH)<(OBJ_SEPARATOR)async-wrap.<(OBJ_SUFFIX)',
             '<(OBJ_PATH)<(OBJ_SEPARATOR)env.<(OBJ_SUFFIX)',