Fix lightkurve link

Lightcurve/Lightcurve tutorial.ipynb

@@ -1903,7 +1903,7 @@
    "source": [
     "## Compatibility with `Lightkurve`\n",
     "\n",
-    "The [`Lightkurve` package](https://docs.lightkurve.org) provides a large amount of complementary functionality to stingray, in particular for data observed with Kepler and TESS, stars and exoplanets, and unevenly sampled data. We have implemented a conversion method that converts to/from `stingray`'s native `Lightcurve` object and `Lightkurve`'s native `LightCurve` object. Equivalent functionality exists in `Lightkurve`, too. The users who have not installed Lightkurve package should do so first by running *pip install lightkurve* in their terminal and then following with the next command."
+    "The [`Lightkurve` package](https://lightkurve.github.io/lightkurve/) provides a large amount of complementary functionality to stingray, in particular for data observed with Kepler and TESS, stars and exoplanets, and unevenly sampled data. We have implemented a conversion method that converts to/from `stingray`'s native `Lightcurve` object and `Lightkurve`'s native `LightCurve` object. Equivalent functionality exists in `Lightkurve`, too. The users who have not installed Lightkurve package should do so first by running *pip install lightkurve* in their terminal and then following with the next command."
    ]
   },
   {