build: Fix build error with python3

Change-Id: Ie90c6a9856b2616131ff9c0c3916aede1978ea94
Refs: #1302
diff --git a/wscript b/wscript
index 080c8c0..dac9432 100644
--- a/wscript
+++ b/wscript
@@ -268,7 +268,7 @@
         cmd = ['git', 'describe', '--always', '--match', '%s*' % GIT_TAG_PREFIX]
         p = Utils.subprocess.Popen(cmd, stdout=Utils.subprocess.PIPE,
                                    stderr=None, stdin=None)
-        out = p.communicate()[0].strip()
+        out = str(p.communicate()[0].strip())
         didGetVersion = (p.returncode == 0 and out != "")
         if didGetVersion:
             if out.startswith(GIT_TAG_PREFIX):