fix a handful of strict null errors; make test config also be strict

These errors only arose because I didn't run `npm build`, only `npm
test`. Then, when I tried building the null checks failed. Keeping the
two config fiels in sync will help prevent this issue in the future

ts/docx/table/grid.ts

@@ -14,6 +14,8 @@ class GridColAttributes extends XmlAttributeComponent<{w: number}> {
 export class GridCol extends XmlComponent {
     constructor(width?: number) {
         super("w:gridCol");
-        this.root.push(new GridColAttributes({w: width}));
+        if (width !== undefined) {
+            this.root.push(new GridColAttributes({w: width}));
+        }
     }
 }

ts/docx/table/index.ts

@@ -23,7 +23,7 @@ export class Table extends XmlComponent {
 
         this.rows = [];
         for (let i = 0; i < rows; i++) {
-            const cells = [];
+            const cells: TableCell[] = [];
             for (let j = 0; j < cols; j++) {
                 cells.push(new TableCell());
             }

ts/test-tsconfig.json

@@ -1,7 +1,12 @@
 {
     "compilerOptions": {
         "target": "es6",
+        "strictNullChecks": true,
+        "sourceMap": true,
+        "removeComments": true,
+        "preserveConstEnums": true,
         "outDir": "../build-tests",
+        "sourceRoot": "./",
         "rootDir": "./",
         "module": "commonjs"
     }

ts/tests/docx/table/testGrid.ts

@@ -15,9 +15,7 @@ describe("GridCol", () => {
         it("does not set a width attribute if not given", () => {
             const grid = new GridCol();
             const tree = new Formatter().format(grid);
-            expect(tree).to.deep.equal({
+            expect(tree).to.deep.equal({"w:gridCol": []});
-                "w:gridCol": [{_attr: {}}],
-            });
         });
     });
 });
@@ -35,13 +33,5 @@ describe("TableGrid", () => {
                 ],
             });
         });
-
-        it("does not set a width attribute if not given", () => {
-            const grid = new GridCol();
-            const tree = new Formatter().format(grid);
-            expect(tree).to.deep.equal({
-                "w:gridCol": [{_attr: {}}],
-            });
-        });
     });
 });