GE Attenuator / Mbed 2 deprecated VAM_DAX_RELIABILITY

update hcsr04.cpp by changing 20000 to 2000

Dependencies:   Stepper mbed SDFileSystem Ultrasonic PinDetect millis

Diff: millis.lib

Revision:
5:938a135613d9
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/millis.lib	Wed Dec 19 19:41:43 2018 +0000
@@ -0,0 +1,1 @@
+https://os.mbed.com/users/hudakz/code/millis/#ac7586424119