config: fix messaging for name symbols

config/config.go

@@ -260,7 +260,8 @@ func (c *Config) Validate() error {
 			// Check that the name matches our regexp
 			if !NameRegexp.Match([]byte(m.Name)) {
 				errs = append(errs, fmt.Errorf(
-					"%s: module name cannot contain special characters",
+					"%s: module name can only contain letters, numbers, "+
+						"dashes, and underscores",
 					m.Id()))
 			}
 		}

terraform/context.go

@@ -1054,8 +1054,9 @@ func (c *walkContext) validateWalkFn() depgraph.WalkFunc {
 			if !config.NameRegexp.Match([]byte(rn.Config.Name)) {
 				l.Lock()
 				meta.Warns = append(meta.Warns, fmt.Sprintf(
-					"'%s' warning: name can't contain special characters.\n" +
-					"this will be an error in Terraform 0.4",
+					"%s: module name can only contain letters, numbers, "+
+						"dashes, and underscores.\n"+
+						"This will be an error in Terraform 0.4",
 					rn.Resource.Id))
 				l.Unlock()
 			}