build: Add RxJava dependency

Author: lpatino10

pom.xml

@@ -49,6 +49,7 @@
         <commons-io-version>2.6</commons-io-version>
         <commons-lang3-version>3.8.1</commons-lang3-version>
         <jersey-version>2.25.1</jersey-version>
+        <rx-version>2.2.7</rx-version>
     </properties>
 
     <!-- we use the travis providers for deployment so don't need to specify repositories here -->
@@ -134,6 +135,11 @@
             <artifactId>gson</artifactId>
             <version>${gson-version}</version>
         </dependency>
+        <dependency>
+            <groupId>io.reactivex.rxjava2</groupId>
+            <artifactId>rxjava</artifactId>
+            <version>${rx-version}</version>
+        </dependency>
     </dependencies>
 
     <build>