evmstate outputs EVMC_LONDON instead of London

[holiman]

For some reason, the output changed into this wonky capital-cased thing:

--- a/evms/testdata/roots/00000006-naivefuzz-0.json.nimbus.stdout.txt
+++ b/evms/testdata/roots/00000006-naivefuzz-0.json.nimbus.stdout.txt
@@ -3,7 +3,7 @@
     "name": "00000006-naivefuzz-0",
     "pass": false,
     "stateRoot": "0xad1024c87b5548e77c937aa50f72b6cb620d278f4dd79bae7f78f71ff75af458",
-    "fork": "London",
+    "fork": "EVMC_LONDON",

diff --git a/evms/testdata/traces/statetest1.json.nimbus.stdout.txt b/evms/testdata/traces/statetest1.json.nimbus.stdout.txt
index 8f2006d..13f9daf 100644
--- a/evms/testdata/traces/statetest1.json.nimbus.stdout.txt
+++ b/evms/testdata/traces/statetest1.json.nimbus.stdout.txt
@@ -3,7 +3,7 @@
     "name": "randomStatetestmartin-Wed_10_02_29-14338-0",
     "pass": false,
     "stateRoot": "0xa2b3391f7a85bf1ad08dc541a1b99da3c591c156351391f26ec88c557ff12134",
-    "fork": "Byzantium",
+    "fork": "EVMC_BYZANTIUM",
     "error": "post state root mismatch: got a2b3391f7a85bf1ad08dc541a1b99da3c591c156351391f26ec88c557ff12134, want 0000000000000000000000000000000000000000000000000000000000000000"
   }
 ]