You quoted from the Holman bible. In your bible you will notice the whole section is placed in square brackets with the footnote "Other manuscripts omit bracketed text".
The most popular and respected bibles versions have the following:
- NASB Whole section is placed in square brackets with the footnote "Later manuscripts add vv 9-20"
- ESV Whole section place in square brackets with the footnote "Some of the earliest manuscripts do not include 16:9–20"
- NIV Whole section is placed in italics below a dividing line with the heading "The earliest manuscripts and some other ancient witnesses do not have verses 9–20."
- RSV Has the following footnote "Mark 16:20 Some of the most ancient authorities bring the book to a close at the end of verse 8. One authority concludes the book by adding after verse 8 the following: But they reported briefly to Peter and those with him all that they had been told. And after this, Jesus himself sent out by means of them, from east to west, the sacred and imperishable proclamation of eternal salvation. Other authorities include the preceding passage and continue with verses 9–20. In most authorities verses 9–20 follow immediately after verse 8; a few authorities insert additional material after verse 14"
But what matters is not whether it appears in your bible, but whether it was written by Mark or by someone else at a later date. The overwhelming consensus among bible scholars is that it is not Mark. The ancient Greek manuscripts in fact have 5 different endings of Mark!
But even if you assume that passage was written by Mark, the prophecy doesn't say believers would continue have those abilities throughout all time. In fact two of the four abilities are conspicuous by their absence today - no doubt because being immune from deadly snake bites and drinking poison are considerably harder to counterfeit than the other two!