Remove usage of ++ outside of for loops update

The usage of postfix ++ is somewhat obscure in its meaning.  It's better
to be explicit here.

test/integration/export.js

@@ -24,7 +24,7 @@ describe("Integration of lib/factorio/export", function() {
 
 				// Value is always a string, nearly always truthy
 				if (!value) {
-					empty_keys++;
+					empty_keys += 1;
 				}
 				assert.equal(typeof value, "string");
 			}

test/lib/factorio/patch.js

@@ -199,7 +199,7 @@ describe("lib/factorio", function() {
 				} catch (err) { }
 				if (success) {
 					validate(modules);
-					successCount++;
+					successCount += 1;
 				}
 			}
 

test/mock.js

@@ -58,10 +58,12 @@ class MockConnector extends events.EventEmitter {
 	}
 
 	send(type, data) {
-		let message = { seq: this._seq, type, data };
+		let seq = this._seq;
+		this._seq += 1;
+		let message = { seq, type, data };
 		this.sentMessages.push(message);
 		setImmediate(() => this.emit("send", message));
-		return this._seq++;
+		return seq;
 	}
 }