docs(operators): fixed references to marble diagrams (#4934)

* fix reference to marble diagram

* fixed reference to marble-diagram: pairs

* updated marble diagram: pairs

* replaced img-tag with md

* replaced img-tag with md

src/internal/observable/generate.ts

@@ -81,7 +81,7 @@ export interface GenerateOptions<T, S> extends GenerateBaseOptions<S> {
  *
  * <span class="informal">Use it instead of nexting values in a for loop.</span>
  *
- * <img src="./img/generate.png" width="100%">
+ * ![](generate.png)
  *
  * `generate` allows you to create stream of values generated with a loop very similar to
  * traditional for loop. First argument of `generate` is a beginning value. Second argument

src/internal/observable/pairs.ts

@@ -8,7 +8,7 @@ import { Subscription } from '../Subscription';
  *
  * <span class="informal">Turn entries of an object into a stream.</span>
  *
- * <img src="./img/pairs.png" width="100%">
+ * ![](pairs.png)
  *
  * `pairs` takes an arbitrary object and returns an Observable that emits arrays. Each
  * emitted array has exactly two elements - the first is a key from the object

src/internal/operators/tap.ts

@@ -23,7 +23,7 @@ export function tap<T>(observer: PartialObserver<T>): MonoTypeOperatorFunction<T
  * <span class="informal">Intercepts each emission on the source and runs a
  * function, but returns an output which is identical to the source as long as errors don't occur.</span>
  *
- * ![](do.png)
+ * ![](tap.png)
  *
  * Returns a mirrored Observable of the source Observable, but modified so that
  * the provided Observer is called to perform a side effect for every value,