apply code review feedback

Author: Alvaro Muñoz

go/ql/lib/semmle/go/frameworks/Twirp.qll

@@ -124,7 +124,7 @@ module Twirp {
     ServerConstructor() {
       exists(ServiceServerType c, ServiceInterfaceType i |
         this.getName().toLowerCase() = "new" + c.getName().toLowerCase() and
-        this.getParameter(0).getType() = i.getNamedType() and
+        this.getParameterType(0) = i.getNamedType() and
         this.getDeclaration().getLocation().getFile() instanceof ServicesGeneratedFile
       )
     }

go/ql/test/library-tests/semmle/go/frameworks/Twirp/tests.expected

@@ -2,9 +2,9 @@ passingPositiveTests
 | PASSED | clientConstructor | rpc/notes/service.twirp.go:53:114:53:139 | comment |
 | PASSED | clientConstructor | rpc/notes/service.twirp.go:192:110:192:135 | comment |
 | PASSED | message | rpc/notes/service.pb.go:23:20:23:35 | comment |
-| PASSED | message | rpc/notes/service.pb.go:86:32:86:49 | comment |
-| PASSED | message | rpc/notes/service.pb.go:133:33:133:50 | comment |
-| PASSED | message | rpc/notes/service.pb.go:171:33:171:50 | comment |
+| PASSED | message | rpc/notes/service.pb.go:86:32:86:47 | comment |
+| PASSED | message | rpc/notes/service.pb.go:133:33:133:48 | comment |
+| PASSED | message | rpc/notes/service.pb.go:171:33:171:48 | comment |
 | PASSED | request | server/main.go:19:111:19:140 | comment |
 | PASSED | request | server/main.go:40:126:40:155 | comment |
 | PASSED | serverConstructor | rpc/notes/service.twirp.go:334:81:334:106 | comment |