JaVers dependency on Google Guava
As documented I just ran the below code to view the diff. It seems that Google Guava is required as a runtime dependency for the below code to work.

```java
Javers javers = JaversBuilder.javers().build();
Person tommyOld = new Person("tommy", "Tommy Smart");
Person tommyNew = new Person("tommy", "Tommy C. Smart");

Diff diff = javers.compare(tommyOld, tommyNew);
System.out.println(diff.prettyPrint());
```
The code above throws an exception as shown below:

```
Exception in thread "main" java.lang.NoClassDefFoundError: com/google/common/collect/ImmutableMap
	at org.javers.core.Changes.<init>(Changes.java:35)
	at org.javers.core.diff.Diff.groupByObject(Diff.java:88)
	at org.javers.core.diff.Diff.toString(Diff.java:129)
	at org.javers.core.diff.Diff.prettyPrint(Diff.java:120)
	...
Caused by: java.lang.ClassNotFoundException: com.google.common.collect.ImmutableMap
	at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
	... 5 more
```

Not sure how the below line of code is used in [org.javers.core.Changes.java](https://github.com/javers/javers/blob/d5ac085c94b5459d464a14ab3e489f31e3c7c110/javers-core/src/main/java/org/javers/core/Changes.java#L35)
There are 3 more references in other classes HibernateConfig.java, JaversSpringJpaApplicationConfig.java and JaversSpringMongoApplicationConfig.java

The above code can be easily replaced with standard Java code to remove dependency on Goolge Guava.

Do let me know if these changes can be done. I will submit a PR.
diff --git a/javers-core/src/main/java/org/javers/common/collections/Primitives.java b/javers-core/src/main/java/org/javers/common/collections/Primitives.java
index eee8a3c4..c9ff294d 100644
--- a/javers-core/src/main/java/org/javers/common/collections/Primitives.java
+++ b/javers-core/src/main/java/org/javers/common/collections/Primitives.java
@@ -1,10 +1,10 @@
 package org.javers.common.collections;
 
-import com.google.common.collect.Streams;
 import org.javers.common.reflection.ReflectionUtil;
 
 import java.util.List;
 import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * @author bartosz walacik
@@ -27,7 +27,7 @@ public class Primitives {
 
     public static List<Class<?>> getPrimitiveAndBoxTypes() {
         return java.util.Collections.unmodifiableList(
-                Streams.concat(PRIMITIVE_NUMBER_TYPES.stream(),
+                Stream.concat(PRIMITIVE_NUMBER_TYPES.stream(),
                                PRIMITIVE_TYPES.stream()).collect(Collectors.toList()));
     }
 
['javers-core/src/main/java/org/javers/common/collections/Primitives.java']