Updated the sky130.tech with a correction for tap diffusion read
from GDS generated using the SkyWater s130 PDK, which eliminates
the TAP layer and uses only DIFF.  One layer type (n-diffusion)
was not handling the use of DIFF for tap diffusion.

VERSION

diff --git a/VERSION b/VERSION
index ae19aa4..7bf92ee 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-1.0.419
+1.0.420

sky130/magic/sky130.tech

diff --git a/sky130/magic/sky130.tech b/sky130/magic/sky130.tech
index cb4cf17..b5c238e 100644
--- a/sky130/magic/sky130.tech
+++ b/sky130/magic/sky130.tech
@@ -2820,7 +2820,7 @@
  and SONOS
  labels DIFF
 
- templayer nsdarea TAP
+ templayer nsdarea TAP,DIFF
  and NSDM
  and NWELL,nwelcheck
  and-not POLY
@@ -2852,7 +2852,7 @@
  templayer xnsubcheck nsubcheck
  copyup nsubcheck
 
- templayer psdarea TAP
+ templayer psdarea TAP,DIFF
  and PSDM
  and-not NWELL,nwelcheck
  and-not POLY
@@ -2942,7 +2942,7 @@
  and-not LVID
  labels DIFF
 
- templayer mvnsdarea TAP
+ templayer mvnsdarea TAP,DIFF
  and NSDM
  and NWELL,nwelcheck
  and-not POLY
@@ -2966,7 +2966,7 @@
  templayer mvxnsubcheck mvnsubcheck
  copyup mvnsubcheck
 
- templayer mvpsdarea DIFF,barediff
+ templayer mvpsdarea TAP,DIFF,barediff
  and PSDM
  and-not NWELL,nwelcheck
  and-not POLY