Updated Guava dependency

Updated Guava dependency to 18.0

org.protege.common/pom.xml

@@ -31,7 +31,7 @@
         <dependency>
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>
-            <version>17.0</version>
+            <version>18.0</version>
         </dependency>
 
         <dependency>

protege-distribution/pom.xml

@@ -131,7 +131,7 @@
         <dependency>
             <groupId>com.google.guava</groupId>
             <artifactId>guava</artifactId>
-            <version>17.0</version>
+            <version>18.0</version>
         </dependency>
 	</dependencies>