build: switch to python3

Refs: #5095
Change-Id: Iedc107d41d4832682071986678b015980354786d
diff --git a/.jenkins b/.jenkins
index 78e1ca1..934aceb 100755
--- a/.jenkins
+++ b/.jenkins
@@ -3,7 +3,7 @@
 
 nanos() {
     # Cannot use date(1) because macOS does not support %N format specifier
-    python -c 'import time; print(int(time.time() * 1e9))'
+    python3 -c 'import time; print(int(time.time() * 1e9))'
 }
 
 for file in .jenkins.d/*; do