Add missing semicolon in binding definition. (tensorflow#119)

I noticed this while working on a design doc today - simple fix :-)

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Author: nkreeger

src/tfjs_binding.d.ts

@@ -45,7 +45,7 @@ export interface TFJSBinding {
   // Executes an Op on the backend, returns an array of output TensorMetadata:
   executeOp(
       opName: string, opAttrs: TFEOpAttr[], inputTensorIds: number[],
-      numOutputs: number): TensorMetadata[]
+      numOutputs: number): TensorMetadata[];
 
   // TF Types
   TF_FLOAT: number;