Allow setting cabal version too

src/installer.ts

@@ -17,10 +17,16 @@ export async function cacheHaskellTool(installDir: string, tool: string) {
 }
 
 export async function findHaskellGHCVersion(version: string) {
+  if (!version) {
+    version = '8.6.5';
+  }
   return _findHaskellToolVersion('ghc', version);
 }
 
 export async function findHaskellCabalVersion(version: string) {
+  if (!version) {
+    version = '3.0';
+  }
   return _findHaskellToolVersion('cabal', version);
 }