fix: ensure randomizationFactor is always between 0 and 1

Using a randomizationFactor value above 1 could lead to generating a
negative duration, then throwing:

> java.lang.IllegalArgumentException: delay < 0: -1012
> at java.util.Timer.schedule(Timer.java:454)
> at io.socket.client.Manager.reconnect(Manager.java:544)

This error does not seem related to a long overflow (in the
BigInteger.longValue() operation), because the BigInteger.min(this.max)
operation before should prevent it.

Related: #349

Author: darrachequesne

Diff for: src/main/java/io/socket/backo/Backoff.java

@@ -3,6 +3,9 @@
 import java.math.BigDecimal;
 import java.math.BigInteger;
 
+/**
+ * Imported from https://github.com/mokesmokes/backo
+ */
 public class Backoff {
 
     private long ms = 100;
@@ -23,7 +26,10 @@ public long duration() {
                     .multiply(new BigDecimal(ms)).toBigInteger();
             ms = (((int) Math.floor(rand * 10)) & 1) == 0 ? ms.subtract(deviation) : ms.add(deviation);
         }
-        return ms.min(BigInteger.valueOf(this.max)).longValue();
+        return ms
+                .min(BigInteger.valueOf(this.max))
+                .max(BigInteger.valueOf(this.ms))
+                .longValue();
     }
 
     public void reset() {
@@ -46,6 +52,10 @@ public Backoff setFactor(int factor) {
     }
 
     public Backoff setJitter(double jitter) {
+        boolean isValid = jitter >= 0 && jitter < 1;
+        if (!isValid) {
+            throw new IllegalArgumentException("jitter must be between 0 and 1");
+        }
         this.jitter = jitter;
         return this;
     }

Diff for: src/test/java/io/socket/backo/BackoffTest.java

@@ -44,4 +44,10 @@ public void durationOverflow() {
             }
         }
     }
+
+    @Test(expected = IllegalArgumentException.class)
+    public void ensureJitterIsValid() {
+        Backoff b = new Backoff();
+        b.setJitter(2);
+    }
 }