fix(Limit): use a parameter for limit number

BREAKING CHANGE: A string expression as the limit number is no longer accepted. The argument must be
a number.

src/clauses/limit.spec.ts

@@ -5,10 +5,12 @@ describe('Limit', () => {
   describe('#build', () => {
     it('should add a produce a limit clause', () => {
       const query = new Limit(10);
-      expect(query.build()).to.equal('LIMIT 10');
+      expect(query.build()).to.equal('LIMIT $limitCount');
+      expect(query.getParams()).to.eql({ limitCount: 10 });
     });
 
-    it('should accept a string param', () => {
+    // TODO re-add in 4.0
+    it.skip('should accept a string param', () => {
       const query = new Limit('toInteger(3 * 4)');
       expect(query.build()).to.equal('LIMIT toInteger(3 * 4)');
     });

src/clauses/limit.ts

@@ -1,11 +1,15 @@
 import { Clause } from '../clause';
+import { Parameter } from '../parameter-bag';
 
 export class Limit extends Clause {
+  protected amountParam: Parameter;
+
   constructor(public amount: number | string) {
     super();
+    this.amountParam = this.addParam(amount, 'limitCount');
   }
 
   build() {
-    return `LIMIT ${this.amount}`;
+    return `LIMIT ${this.amountParam}`;
   }
 }