Remove Go 1.11, 1.12 from CI; change lowest supported Go version to 1.13

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
     strategy:
       matrix:
         java-version: ['8', '11', '12', '13', '14', '15', '16']
-        golang-version: ['1.11', '1.12', '1.13', '1.14', '1.15', '1.16']
+        golang-version: ['1.13', '1.14', '1.15', '1.16']
 
     steps:
     - uses: actions/checkout@v2

README.md

@@ -130,4 +130,6 @@ PGo's Go runtime library depends on:
   For example, creating a modified map with one different key-value pair should take constant time, rather than copy the
   entire existing structure.
 
-PGo is tested using OpenJDK 1.8, 1.11 through 1.16, and Go 1.11 through 1.16.
+PGo is tested using OpenJDK 1.8, 1.11 through 1.16, and Go 1.13 through 1.16.
+Go >=1.13 is needed because of [changes to the errors package in that version](https://blog.golang.org/go1.13-errors),
+and, otherwise, Go >=1.11 is needed due to the use of Go modules.

distsys/go.mod

@@ -1,5 +1,5 @@
 module github.com/UBC-NSS/pgo/distsys
 
-go 1.14
+go 1.13
 
 require github.com/benbjohnson/immutable v0.3.0

test/files/general/ExprTests.tla.gotests/go.mod

@@ -1,6 +1,6 @@
 module example.org/exprtests
 
-go 1.14
+go 1.13
 
 replace github.com/UBC-NSS/pgo/distsys => ../../../../distsys
 

test/files/general/dqueue.tla.gotests/go.mod

@@ -1,6 +1,6 @@
 module example.org/dqueue
 
-go 1.14
+go 1.13
 
 replace github.com/UBC-NSS/pgo/distsys => ../../../../distsys
 

test/files/general/load_balancer.tla.gotests/go.mod

@@ -1,6 +1,6 @@
 module example.org/load_balancer
 
-go 1.14
+go 1.13
 
 replace github.com/UBC-NSS/pgo/distsys => ../../../../distsys
 

test/files/general/replicated_kv.tla.gotests/go.mod

@@ -1,6 +1,6 @@
 module example.org/replicated_kv
 
-go 1.14
+go 1.13
 
 replace github.com/UBC-NSS/pgo/distsys => ../../../../distsys