Updates nimble commit (#25036)

(cherry picked from commit 370ee61)

Author: jmgomez

koch.nim

@@ -11,7 +11,7 @@
 
 const
   # examples of possible values for repos: Head, ea82b54
-  NimbleStableCommit = "b1dc28450f028aead0b7cf5da8adf2267db65f89" # 0.18.2
+  NimbleStableCommit = "6a2486b597132340ea7422b078c769b58f21d16d" # 0.20.0
   AtlasStableCommit = "26cecf4d0cc038d5422fc1aa737eec9c8803a82b" # 0.9
   ChecksumsStableCommit = "f8f6bd34bfa3fe12c64b919059ad856a96efcba0" # 2.0.1
   SatStableCommit = "faf1617f44d7632ee9601ebc13887644925dcc01"