fail to parse config text with white space
- [ ] I have searched the [issues](https://github.com/apache/incubator-dubbo/issues) of this repository and believe that this is not a duplicate.
- [ ] I have checked the [FAQ](https://github.com/apache/incubator-dubbo/blob/master/FAQ.md) of this repository and believe that this is not a duplicate.

### Environment

* Dubbo version: 2.7.0
* Operating System version: Mac OS
* Java version: JDK1.8

### Steps to reproduce this issue

1. create `dubbo.properties` with trailing white space  
```properties
dubbo.provider.timeout=6666    
```
2. start dubbo provider  
3. will cause an exception: 
```java
java.lang.NumberFormatException: For input string: "6666   "
	at java.lang.NumberFormatException.forInputString(NumberFormatException.java:65)
	at java.lang.Integer.parseInt(Integer.java:580)
	at java.lang.Integer.valueOf(Integer.java:766)
	at org.apache.dubbo.common.utils.ClassHelper.convertPrimitive(ClassHelper.java:277)
	at org.apache.dubbo.config.AbstractConfig.refresh(AbstractConfig.java:568)
	at java.util.concurrent.ConcurrentHashMap$ValuesView.forEach(ConcurrentHashMap.java:4707)
	at org.apache.dubbo.config.context.ConfigManager.refreshAll(ConfigManager.java:308)
	at org.apache.dubbo.config.AbstractInterfaceConfig.startConfigCenter(AbstractInterfaceConfig.java:241)
	at org.apache.dubbo.config.ServiceConfig.checkAndUpdateSubConfigs(ServiceConfig.java:267)
	at org.apache.dubbo.config.ServiceConfig.export(ServiceConfig.java:328)
	at org.apache.dubbo.config.spring.ServiceBean.onApplicationEvent(ServiceBean.java:104)
	at org.apache.dubbo.config.spring.ServiceBean.onApplicationEvent(ServiceBean.java:55)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
	at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:400)
	at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:354)
	at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:886)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.finishRefresh(ServletWebServerApplicationContext.java:161)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:386)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:307)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1242)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1230)
	at org.apache.dubbo.demo.DubboProviderApplication.main(DubboProviderApplication.java:13)
```

Pls. provide [GitHub address] to reproduce this issue.

### Expected Result

What do you expected from the above steps？

### Actual Result

What actually happens?

If there is an exception, please attach the exception trace:

```
Just put your stack trace here!
```