Add serialVersionUID to exceptions.

Author: Capstan

build.gradle

@@ -127,7 +127,7 @@ task sourcesJar(type: Jar, dependsOn: classes) {
 allprojects {
     gradle.projectsEvaluated {
         tasks.withType(JavaCompile) {
-            options.compilerArgs << "-Xlint:all" << "-Xlint:-serial" << "-Werror"
+            options.compilerArgs << "-Xlint:all" << "-Werror"
         }
         tasks.withType(Javadoc) {
             options.addStringOption('Xwerror', '-quiet')

src/main/java/com/github/fge/avro/IllegalAvroSchemaException.java

@@ -24,6 +24,7 @@
 public final class IllegalAvroSchemaException
     extends ProcessingException
 {
+    private static final long serialVersionUID = 2922864168105819839L;
     private static final String ILLEGAL = "illegal Avro schema";
 
     public IllegalAvroSchemaException(final Throwable e)

src/main/java/com/github/fge/jsonschema2avro/UnsupportedJsonSchemaException.java

@@ -24,4 +24,5 @@
 public final class UnsupportedJsonSchemaException
     extends ProcessingException
 {
+    private static final long serialVersionUID = -4913037914523960446L;
 }