Start error messages with a capital letter

Author: erayd

src/JsonSchema/Constraints/SchemaConstraint.php

@@ -48,7 +48,7 @@ public function check(&$element, $schema = null, JsonPointer $path = null, $i =
         // schema is defined, assume self::DEFAULT_SCHEMA_SPEC (currently draft-04).
         if ($this->factory->getConfig(self::CHECK_MODE_VALIDATE_SCHEMA)) {
             if (!$this->getTypeCheck()->isObject($validationSchema)) {
-                throw new RuntimeException('cannot validate non-object schema');
+                throw new RuntimeException('Cannot validate non-object schema');
             }
             if ($this->getTypeCheck()->propertyExists($validationSchema, '$schema')) {
                 $schemaSpec = $this->getTypeCheck()->propertyGet($validationSchema, '$schema');
@@ -76,7 +76,7 @@ public function check(&$element, $schema = null, JsonPointer $path = null, $i =
             $validator->validate($validationSchema, $schemaStorage->getSchema($schemaSpec));
             if (!$validator->isValid()) {
                 $this->addErrors($validator->getErrors());
-                $this->addError($path, 'schema is not valid', 'schema');
+                $this->addError($path, 'Schema is not valid', 'schema');
             }
         }